History.md fixes

Made few fixes for [history.md](http://jekyllrb.com/docs/history/)

- Fix messed up list items
    
![2014-05-08_messed_up_list_items](https://cloud.githubusercontent.com/assets/1937586/2911402/caf7fb80-d65a-11e3-90d3-757e0210f817.png)

- Fix parsing issues with two consecutive hyphens, like "--some_option"
    
![2014-05-08_parsing_two_consecutive_hyphens](https://cloud.githubusercontent.com/assets/1937586/2911403/ce29c2ac-d65a-11e3-971d-5823c0f4af6f.png)

- Capitalize word "jekyll" in appropriate situations