Start changing the text parsing architecture
Extract all the text processing into a superclass: KMTextParser
Recursively commit the parsers
Rename the main file system folder and the Xcode group to KMTextParser
Update README with new public API for KMMarkdownParser
Use the default font if one hasn't been specified

This meant having to change the processing block API slightly
so that the text parser can have access to all the information about the attributes