to `rebar_erlc_compiler`

In the scenario we that we have selected a commit
that is between two tags, we should base the
version on the most recent tag we can see in the
revision history, but we should not treat this as
the tag version.

`git describe --tags --abbrev=0` finds the most
recent tag visible in the revision history from
the current HEAD. Return this as the version
string and undefined as the tag to trigger ref
counting.

In the scenario that someone had cloned an entire
repository and then checked out an older version
tag, the semantic versioning would detect the
newest tag, not the checked out tag. Look for
the HEAD string prior to tag: to indicate the
currently selected tag.

Version #'s with patch info like "1.1.1-x" would cause an error. Now
tokenize the version string with "." AND "-".

In the scenario we that we have selected a commit
that is between two tags, we should base the
version on the most recent tag we can see in the
revision history, but we should not treat this as
the tag version.

`git describe --tags` finds the most recent tag
visible in the revision history from the current
HEAD. Return this as the version string and
undefined as the tag to trigger ref counting.

In the scenario that someone had cloned an entire
repository and then checked out an older version
tag, the semantic versioning would detect the
newest tag, not the checked out tag. Look for
the HEAD string prior to tag: to indicate the
currently selected tag.

Not all repositories use a v-prefix for version
tags. All tags should be considered valid
versions.

`reduce_path/1` -> `canonical_path/1`
`relative_path/2` -> `path_from_ancestor/2`

add tests

Fixes compiling yaws, which has an .app.src.script file

fixes #788