Make more files available without native ext to fix CLI
Version bump
Update CHANGELOG
Update CHANGELOG for 0.3.1
Fix failing tests with Ruby 1.9.3+

It looks like the rb_enc_associate function we were relying was moved
into ruby/encoding.h in a later release. This fix imports the
appropriate header file.
Merge branch 'maint/0.3.1'
Autoload helpers even without native agent
Bump version