Bundler integeration, test updates, and other minor changes

[pcting]

1. Added support for bundler:
   $ git clone ... && cd ./log4r_checkout/
   $ bundle update
   $ bundle exec rake test
   $ bundle exec rake install
   $ bundle exec rake build
2. Migrated to a gemspec file
3. I was wrapping my custom exceptions without the backtrace set and found out i was getting errors so i made this patch

[pcting]

so i added a massive change. hopefully it's something you're interested in. so i updated the code to work with bundler. To setup your environment:
$ git clone ... && cd ./log4r_checkout/
$ bundle update
$ bundle exec rake test
$ bundle exec rake install
$ bundle exec rake build

let me know what you think

[pcting]

oh ya... so all the tests run, but not all of them pass as the tests are quite out dated. I had to change all the "assert_no_exception" methods to "assert_nothing_raised" and "assert_exception" to "assert_raise" along with other tweaks to get the tests to run