modular versioning

[bluegenes]

Perhaps we'd like to enable easy version choice?

Local option: whenever we update the version, we could keep the old environment.yml file as a named version, e.g. environment_0.2.0.yml. Then add a "version" key to the program_params for each program, which can be used to switch the environment (and potentially wrapper, if major syntax changes) used to run the program.

Alternatively: work on improving version tracking in snakemake-wrappers repo, and figure out how to link program version: wrapper number/info. As all our wrappers are currently local to elvers, we would need to upload our additional (and modified) wrappers to the the wrappers repo.