Removed rails2 compatibility
Fix the way we fetch jobs to work better for a large number of workers.

Instead of fetching 5 candidates at attempting to lock each one by one, just lock the next job in 1 query.

Example of old system and 100 workers (worst but not uncommon case):
1) 100 workers wake up and fetch 5 candidate jobs (they all get the same, or very similar set of 5 jobs), making a total of 100 SELECT calls
2) they all try to lock the first job (only 1 of 99 succeeds). The failing workers try the next, making a total of roughly 500 UPDATE calls
3) a total of 5 jobs get processed from about 600 database calls, and we restart the whole process

New system:
1) 100 workers wake up and fetch the next available job, each getting a single unique job (1 SELECT and 1 UPDATE call each).
2) a total of 100 jobs are processed with exactly 200 SQL calls

I've also included an example to make it all work in 1 call, avoiding an extra round-trip. This requires custom SQL only tested with PostgreSQL
Test against Ruby 2.0.0
Convert text files to Markdown
Even faster for postgresql
Specify minimum rspec version
Don't test against JRuby
Merge pull request #29 from scosman/master

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Merge pull request #26 from rwz/master

Removed rails 2 compatibility
No need to check for Rails 3
Prep for release 0.4.0
Add Gem Version badge [ci skip]
Add Code Climate badge [ci skip]
Test against multiple database adapters
Test against JRuby
Don't allow failure on Rubinius
Possible fix for MySQL support
Prep for release 0.4.1
The source :rubygems is deprecated because HTTP requests are insecure.
Fix misstypo quote_column_name to quote_table_name