Added .gitattributes file for crlf issues
Added StudentTestCase, which captures output data.

This deals with automatically replacing the streams and capturing the
data sent to stdout and stderr.

It's possible that we need to replace input() itself properly, or at
least consider how to handle EOF on stdin; this will be necessary when
students ask for more data than they should.
Removed output and error redirection.
Can now exec submodules with globals and locals
Gave TESTS_MODULE access to StudentTestCase
Tests will now run (but full implementation WIP)
Added CodeAnalyser and refactored analysis.

It is cleaner for the CodeAnalyser to get a reference to the CodeVisitor
upon creation, in order to limit the amount of variables that have to be
extracted from the compiled file.
Added explanation of the dangers with exec_module

This reflects problems encountered in using a reference to CodeVisitor
from a CodeAnalyser subclass.
Fixed up the PEP8 error suppression