Cleanup rounding increment usages with new struct

[jedel1043]

Cleans up all usages of the rounding increment so that all have to pass through RoundingIncrement, increasing strictness.
Also moves the RoundingIncrement struct from options.rs to its own increment.rs file

[nekevss]

Can you move RoundingIncrement to a rounding.rs file. I'm hoping that may make the rebase a little easier. I'm also then not moving it over from options.rs to rounding.rs