Add hex_version module

[wojtekmach]

Since all package versions follow semver, we should add functions to encode/decode and compare them. I think we should simply vendor in https://hexdocs.pm/verl though let's make sure we expose as small API as possible, we can grow it later.

[essen]

As far as Erlang.mk is concerned, the is_match function with version and requirement as binaries, are all that is necessary. The equivalent to Elixir.Version:match?.