Fixes #1

Refactored to limit text based input styling scope to avoid styling checkboxes and radio buttons and anything else that isn't a text input.

- Preview of the updated docs: http://himedlooff.github.io/cf-forms/docs/.
- Preview of the updated demo: http://himedlooff.github.io/cf-forms/demo/ (notice how I added a checkbox and radio button to make sure the styles aren't too aggressive).

The method I used to fix this was to use the [extend method in Less](http://lesscss.org/features/#extend-feature). This allows us to have a docs section on each input type while keeping the amount of duplicate CSS to a minimum. To get here required a little bit of refactoring for form icon usage. You now have to specify `.cf-form_input-icon` on each icon that you want to use after a text input. This keeps base styling for form icons a little easier to target. This also allows us to have a nice little docs section on form icon usage.