Add a TOML Lexer

# TOML

>TOML aims to be a minimal configuration file format that's easy to read due to obvious semantics. TOML is designed to map unambiguously to a hash table. TOML should be easy to parse into data structures in a wide variety of languages. https://github.com/mojombo/toml

Until TOML reaches a 1.0 release, this should be considered a work in progress.

## Still to do

- [ ] Multiline Arrays (https://github.com/mojombo/toml#array) aren't working
![localhost_9292_toml](https://f.cloud.github.com/assets/205556/204862/ef13c09e-818d-11e2-8c3e-c25715d80616.png)
- [ ] "double comments" (# foo # bar) aren't working
![localhost_9292_toml-1](https://f.cloud.github.com/assets/205556/204866/0ecda152-818e-11e2-899f-a458ddc828d5.png)
- [ ] `Lexer#guess_by_source` can't properly differentiate between INI and TOML because they are to similar and I couldn't come up with two good regexes :/ (see test on [Travis](https://travis-ci.org/coffeejunk/rouge/jobs/5128750))  
I believe both `self.analyze_text` methods (for INI and TOML) have to be pimped a bit.