Improve ShortVersionParser.TryParseMajorMinor() test coverage
Refactor ShortVersionParser.TryParseMajorMinor()
Enforce NewestSemVerTag() test coverage
Fix indentations
Make NewestSemVerTag() cope with unordered tags

IRepository.Tags doesn't enforce the order of the returned tags. Indeed, the order depends
on the way the OS and (the underlying storage system) return entries in a directory.
Refactor MergeMessageParser.TryParse() related tests
Make MergeMessageParser.TryParse() detect invalid merge commits

A commit is said to be a "merge commit" if it bears more than one parent commit.
Merge pull request #36 from nulltoken/ntk/fix/miscellanea

Various minor enhancements