Add increment behaviour to Version class

Allows the incrementing of major, minor and patch identifiers with
appropriate side effects and the independent setting of pre and build
identifiers.
Add VersionSet class

A VersionSet is a sorted set of Version instances. Duplicates are ignored,
versions are yielded in order and a method (version_set#where) is provided for
querying the set.
Update version and gemspec

Version 0.1.0 and some better description text / file globbing.