Fix #1: can't add a new key during iteration

In Ruby 1.8, you could insert into hashes while iterating, but since 1.9
uses ordered hashes, this results in a RuntimeError. The fix is to
convert the hash to an array before iteration.

This change is from http://stackoverflow.com/a/11120147/73492, but it
was never reported back to the project.
Replace jeweler with bundler
Fix deprecated error: rake/rdoctask => rdoc/task
Replace rcov with simplecov

Rcov doesn't run on 1.9+, but simplecov is a good replacement. Coverage
reports are now generated automatically with `rake test'.

I also removed the empty unit test in `test/helper.rb' too.
Merge pull request #3 from jmdeldin/fix-adding-key-during-iteration-bug

Fix #1: can't add a new key during iteration
Merge pull request #4 from jmdeldin/move-devel-to-19

Update development environment for 1.9