Gemspec much more automated.

Breaks version into its own file typingpool/version.rb.

Gemspec loads version file from neighboring lib/ and uses the version
defined within that to build the gem, whereas previously we were
typing it in two places. Loads file list from git, whereas previously
I was worried about the dependency (which is silly as only people who
want to actually re-build the gem will need git). Sets date
dynamically by calling Time.now.

This is the sort of shit I always forget so it's best that it's now
done automatically (like everyone else does it).