Up the CI game (#21)

* Up the CI game

* bump rebar3_lint

* introduce rebar3_hank

* Prevent a dialyzer warning on a consumer lib which happens to be rebar3_hex

Setup for publishing docs to hex using ex_doc (#18)

Make all types open vs opaque (#15)

- Historically types such as version_t(), requirement_t(), etc. were
 opaque. This surely made sense when it was not clear if the internals
 would change. I think it's safe to say at this point semver2 is more or
 less set in stone and that these types will not change.

Merge pull request #6 from paulo-ferraz-oliveira/potential_improvements

Potential improvements

bump patch version in app.src

Fix indentation

be more specific in descrip