Add support for list tag helpers, and convert other helpers to use them

Also add support for pill-style navigation in tabs helper
Add method hook for creating unknown tags by default, removes need for p() and h4()
Add note about Font Awesome version dependency

Apply defaults for submit button to nicely allow overrides, fix attri…

…butes cast to array from object

Let headings have arbitrary attributes from opts

Code clean-up

Add support for buttons

Initial commit