index.html: remove 'Index of'
lexington.py: clean up comments and docstrings
lexington.py: generate a root index.html file
Node.process: skip comments and directives

Will eventually add directive handling, but for now just skip them.
Node.render: fall back to 'default.html' when rendering
Node.safe_filename: check for parent before creation
Node.process: check if final node is summit
base.html: be smarter about including head.longTitle
lexington.py: better method of generating index children

The xpath method could have gotten hairy for checking @type, but this
is much clearer.
Node.render_nodetypes: only render outline node types
Node.body: wrap as appropriate

All nodes get wrapped in paragraph tags and when an element has
children, wrap it in a <div class=sub>...</div> container.
Node: make attributes available in 'attrib'
templates: add some style

Bootstrap 3, Font Awesome, Bootswatch. It's all here.