build: import erlang.mk

- uses erlang.mk with upstream patch #139 for common_test support
- removes script creation but this can be added into erlang.mk relatively easily
docs: update for new build process
build: reindent tests too
Merge pull request #25 from skunkwerks/feature/use-erlang.mk

build: use erlang.mk instead of rebar

- uses erlang.mk with upstream patch #139 for common_test support
- removes script creation but this can be added into erlang.mk relatively easily (see #24 )
- needs to be able to include the git sha in `.app.src` file either in `{vsn, ...}` or in `{id, ...}`