Add option to obey autoescape in Jinja2 context

Default behavior is unchanged with this commit.

If the user passes autoescape=True to the Markdown constructor,
usage of the |markdown filter in Jinja2 templates will now
autoescape the content before passing it along to Markdown if
autoescape is enabled in the current evaluation context, as it
is by default in Flask for common template extensions (.html,
.htm, .xml, and .xhtml).

This commit also reworks the nose tests to use module- and test-
level setup and teardown functions to prevent conflicts with the
@app.route decorator.
Merge branch 'master' of github.com:tthieman/flask-markdown into integration

Conflicts:
	tests/test_markdown.py
Remove dependency on app config for markdown instance

The usage of app config allowed the behavior of a markdown instance to
be modified during the application's lifecycle. Once the markdown
extension is instantiated, its behavior should not be modifiable.

* Apply PEP8
* Clean up test state with injection of fixture
* Update a few docs
Merge pull request #8 from dcolish/integration

Finish integrating auto escape obedience feature