Additional CSS to improve appearance

- centered/bolded rubric text
- added spacing between tables
- improved table headers
- coloured system message heading
- right-aligned sidebars
- more block-level item styles
Improved syntax highlighting
If Pygments is installed, Python doctest blocks or code, code-block, or
sourcecode blocks specifying a language will be syntax-highlighted.
Styles are set in a <style> block in the document's <head>.
Allow serving images with .gif & .jpeg extensions
Improved HTTP error messages
Fixes for HTML output

- added header to prevent browsers from caching HTML response
- only append the script block if reading a file
- if a command was specified, set it as the page title
Improvements for directory listing

- skip any directory starting with a dot
- ignore case when sorting contents
- print absolute path to the directory
- include a doctype
Better auto-refresh behaviour

- uses long polling to refresh the browser when the source file is modified
- avoids looping issues by keeping only one request open at a time
- restores ability to pass multiple file arguments to restview
Use as for Python 3 compatibility
deleted unnecessary line
Highlighting fix for docutils 0.10
Some changes suggested by pyflakes

Also reset highlight style to default.
Merge pull request #4 from EricFromCanada/master

Fixes/improvements in formatting, highlighting, & auto-refresh