Backwards compatibility ftw

This release just re-implements Gem::Specification#lib_dirs_glob
internally, using features that were added to Rubygems a decade ago, for
people who are using very old versions of Rubygems.

Bugfixes: the UnwashedMeme edition

Fixed a typo and 1.8 compatibility problems. Thanks to @UnwashedMeme for
the patches.

Fix 'Version is now' output

One more place I needed to pass 'true' into GVB.version...

Other projects have versions too, you know

This release changes the API by re-adding an optional argument to
GVB.version and GVB.date, to tell them to not do anything clever (looking in
the call stack) to find out who's calling, but instead only look in the
local git tree. This is needed for git-version-bump (the binary) to
recognise versions other than GVB's own.

The "robustness" release

Hopefully less unwanted exceptions will be raised, however some more useful
exceptions may be raised instead.

Syntax...

This is why I should have a test suite.

Helpful and bugless

One new feature: Show the version tag in the commentary to the version, so
that you know what version you're writing the release notes for.

And one bugfix: If you invoked a program or library and you weren't in the
git repo, then GVB wouldn't be able to work out the version from the git
info. Now it can.

Version 0.9.1: The "how does 'or' work, again?" release

Just a patch to make the --notes option be recognised as an alias for -n.

Version 0.9.0

This release adds a very neat new feature: editing the annotation that goes
along with the release tag. This allows you to add release notes, which,
alongside the newly-released github-release gem (which provides a handy-dandy
git release command), makes uploading a new release to github very easy.

Version v0.8.0

Version v0.8.0