Release workflow

[tvercaut]

MONAI needs to follow good practice for its versioning system and release workflow.

Versions should be numbered following Semantic Versioning (semver). Versioneer can help for this. See e.g. how it is used in NiftyNet

The package should be published on pypi.

Documentation for project admins should bee provided. Niftynet has some example that can use as starting point.

[pdogra89]

@IsaacYangSLA - would work with NVIDIA team and come up with a proposal.