Conslidate template rendering methods.

Was using CodeClimate with my own Sinatra application, and stumbled upon Sinatra's CodeClimate analysis.
I saw the following there:

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![sinatra_duplication_codeclimate](https://f.cloud.github.com/assets/3589911/1897955/977811b0-7c04-11e3-8f2f-f92a57e4103b.png)

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This pull request will eliminate those two duplication issues from the code base by:

- Placing relevant methods together and defining them via `define_method`.
- Re-ordering methods within the module based on what they are rendering.

Ran the full, built-in test suite via `rake test` and had all tests pass.