Merge pull request #1 from dblock/gitignore

Gitignore only files that actually exist in this repo.
Merge pull request #2 from dblock/uzs

Added support for currencies that don't have a symbol, eg. Uzbekistan Som (UZS).
Updated README.md title
Changed symbol truthiness checks to symbol.present?
Removed duplicate tests for number_only=true
Bumped version to 0.0.3
Updated description wording from 'class' to 'module'
Fixed typo in README.md
Relax dependency on ActiveSupport 3.x.