Add setContent and fix clean firstChild bug

The setContent receives a HTML string, cleans it and sets it as the innerHTML of the editor.

The bug was with cleaning HTML, where the first children were not being wrapped in segments. Each node either remained a block-level tag or was converted into a p tag. If there is a series of inline-level nodes they should be combined together before being wrapped in the p tag.

Initial development release

This release is to get the code out there for integration testing. Bold, italicize and tag hierarchy detection (for toolbar highlighting) work well, but other elements need refinement.