Add a script to clear outputs from notebooks

Currently, it only supports in-place conversion.
add IPython lexer for pygments
add some basic css/js for HTML export
Add true HTML export

This adds full HTML export with notebook css, etc.

todo:

Figures are inlined, and foo_files/image.png mode should probably be available as an option.

MathJax is still loaded from a CDN, and should probably be configurable (or disabled).

We could probably trim most of the CSS, so we just have what we need, but that would mean maintaining some synchronization with upstream CSS probably.
Merge pull request #18 from tkf/nbstripout

Add a script to clear outputs from notebooks
Merge pull request #19 from minrk/html

Add further HTML export
use markdown package instead instead of subprocess
fix utf8, add utf8 in html headers
Merge pull request #26 from Carreau/utf8fix

fix utf8 for html output.

This hardcode utf-8 in html templates
remove redundant docstrings with @DocInherit
added 'py' format, which is cleaner than PyWriter

additionally, it allows for future extensions (where you drop the prompt
numbers, or all of the markdown cells, or drop just the code and keep
only the markdown around as comments, as a template for homework, for
example).

Currently, as noted in ConverterPy's docstring, it does not guarantee
that what gets written is valid python, since the code cells may contain
magics.
Merge pull request #25 from Carreau/no_md_subprocess

use markdown package instead instead of subprocess
Merge pull request #28 from ivanov/doc-inherit

remove redundant docstrings with @DocInherit
Merge pull request #29 from ivanov/write-py

added 'py' format, which is cleaner than PyWriter
Note pandoc requirement in readme.
Add usage note.
Installing docutils requires tgz extension

In order to get pip to recognize that docutils was a tar.gz, I needed to make the extension .tgz or .tar.gz, so update the instructions.
Merge pull request #34 from jasongrout/patch-1

Installing docutils requires tgz extension
Fix extension in README instructions
Small cleanup/bugfix in in_tag method for html converter.

Fix missing quotes and spaces in in_tag, avoid a += string loop.
Also, fix missing quotes in header.