Remove build-in editor and preview
Remove custom TreeModel
Start porting to Gtk3
Start porting to Python3
Move GtkTreeModel management to the site module
Merge building files index and tree model
Mark internal functions of Site class with leading underscore
Remove File.url property
Remove Style class
Remove Template class
Update included smartypants
Remove file contents reading and writing from the File class
Convert tests to Python3
Remove multicast signaling from site package

GtkTreeModel would be modified directly
Monitor filesystem for new and removed files
Make indexes protected members
Replace old HTML generator with new converters mechanism

This also changes format of pages and templates:
Pages now must have extension .md or .markdown
Templates use the jinja2 engine
Remove CLASSES dictionary separate classes for file types are not used anymore
Remove separate templates tree view
Remove separate templates list in site model

Also remove old site tests as they are no longer valid