docs: Added a list of all possible hash algorithms and default hash function (#357)

* Added a link to the list of possible values for hash/hashAlg
* Added the link to the list of all possible hash functions as well as the default hash algorithm

Author: aleybovich

SPEC/FILES.md

@@ -156,7 +156,7 @@ If no `content` is passed, then the path is treated as an empty directory
 - cid-version (integer, default 0): the CID version to use when storing the data (storage keys are based on the CID, including it's version)
 - progress (function): a function that will be called with the byte length of chunks as a file is added to ipfs.
 - recursive (boolean): for when a Path is passed, this option can be enabled to add recursively all the files.
-- hashAlg || hash (string): multihash hashing algorithm to use.
+- hashAlg || hash (string): multihash hashing algorithm to use. (default: `sha2-256`) [The list of all possible values]( https://github.com/multiformats/js-multihash/blob/master/src/constants.js#L5-L343)
 - wrapWithDirectory (boolean): adds a wrapping node around the content.
 - onlyHash (boolean): doesn't actually add the file to IPFS, but rather calculates its hash.
 - pin (boolean, default true): pin this object when adding.
@@ -217,7 +217,7 @@ Returns a Readable Stream of class Duplex, where objects can be written of the f
 
 - cid-version (integer, default 0): the CID version to use when storing the data (storage keys are based on the CID, including it's version)
 - progress (function): a function that will be called with the byte length of chunks as a file is added to ipfs.
-- hashAlg || hash (string): multihash hashing algorithm to use
+- hashAlg || hash (string): multihash hashing algorithm to use. (default: `sha2-256`) [The list of all possible values]( https://github.com/multiformats/js-multihash/blob/master/src/constants.js#L5-L343)
 - wrapWithDirectory (boolean): adds a wrapping node around the content
 - pin (boolean, default true): pin this object when adding.
 
@@ -267,7 +267,7 @@ Returns a Pull Stream, where objects can be written of the forms
 
 - cid-version (integer, default 0): the CID version to use when storing the data (storage keys are based on the CID, including it's version)
 - progress (function): a function that will be called with the byte length of chunks as a file is added to ipfs.
-- hashAlg || hash (string): multihash hashing algorithm to use
+- hashAlg || hash (string): multihash hashing algorithm to use. (default: `sha2-256`) [The list of all possible values]( https://github.com/multiformats/js-multihash/blob/master/src/constants.js#L5-L343)
 - wrapWithDirectory (boolean): adds a wrapping node around the content
 - pin (boolean, default true): pin this object when adding.
 
@@ -618,7 +618,7 @@ Where:
 - `options` is an optional Object that might contain the following keys:
   - `parents` is a Boolean value to decide whether or not to make the parent directories if they don't exist (default: false)
   - `format` is what type of nodes to write any newly created directories as (default: `dag-pb`)
-  - `hashAlg` is which algorithm to use when creating CIDs for newly created directories (default: `sha2-256`)
+  - `hashAlg` is which algorithm to use when creating CIDs for newly created directories. (default: `sha2-256`) [The list of all possible values]( https://github.com/multiformats/js-multihash/blob/master/src/constants.js#L5-L343)
   - `flush` is a Boolean value to decide whether or not to immediately flush MFS changes to disk (default: true)
 - `callback` is an optional function with the signature `function (error) {}`, where `error` may be an Error that occured if the operation was not successful
 
@@ -671,7 +671,7 @@ Where:
 - `options` is an optional Object that might contain the following keys:
   - `parents` is a Boolean value to decide whether or not to make the parent directories if they don't exist  (default: false)
   - `format` is what type of nodes to write any newly created directories as (default: `dag-pb`)
-  - `hashAlg` is which algorithm to use when creating CIDs for newly created directories (default: `sha2-256`)
+  - `hashAlg` is which algorithm to use when creating CIDs for newly created directories (default: `sha2-256`) [The list of all possible values]( https://github.com/multiformats/js-multihash/blob/master/src/constants.js#L5-L343)
   - `flush` is a Boolean value to decide whether or not to immediately flush MFS changes to disk  (default: true)
 - `callback` is an optional function with the signature `function (error) {}`, where `error` may be an Error that occured if the operation was not successful
 
@@ -911,7 +911,7 @@ Where:
 - `options` is an optional Object that might contain the following keys:
   - `parents` is a Boolean value to decide whether or not to make the parent directories if they don't exist (default: false)
   - `format` is what type of nodes to write any newly created directories as (default: `dag-pb`)
-  - `hashAlg` is which algorithm to use when creating CIDs for newly created directories (default: `sha2-256`)
+  - `hashAlg` is which algorithm to use when creating CIDs for newly created directories (default: `sha2-256`) [The list of all possible values]( https://github.com/multiformats/js-multihash/blob/master/src/constants.js#L5-L343)
   - `flush` is a Boolean value to decide whether or not to immediately flush MFS changes to disk (default: true)
 - `callback` is an optional function with the signature `function (error) {}`, where `error` may be an Error that occured if the operation was not successful