Initial messing around.

Latex tab completion will have to be done outside the normal
completer logic as the completer line splitting logic uses
\\ as a special character to split lines on. I probably want
to put the latex completions first and it if finds any matches,
don't do any other completion logic. The only issue is that might
short circuit dir/path matching on windows. Hmmm.
Adding autogenerated latex_symbols.py.
Adding regexp for unicode identifers to CM mode.
Initial implementation of latex->unicode completer.
Cleaning up and only doing latex completion for python 3.
Adding partial latex completions.
Adding tests and limiting CM mode to python 3.
Adding latex_symbols.ipynb.
Adding script to generate latex_symbols.py.
Updating gen_latex_symbols.py
TEST: Fix invalid ast transformer in test.

The ast transformer used in test_interactiveshell.TestAstTransformError
had an incorrect method signature, causing it to raise a TypeError when
called, rather than the expected ValueError.  This change makes the test
transformer actually throw the expected error.
DEV: AST transformers supplied to `InteractiveShell` can reject input.

* Adds a new exception class, `InputRejected` to IPython.lib.security.
* Updates `InteractiveShell.run_cell` and
  `InteractiveShell.transform_ast` to allow user-supplied AST
  transformers to reject input by raising an `InputRejected`.
* Adds tests for the above behavior.
MAINT: Move `InputRejected` to `IPython.core.error`.
BUG: Explicitly close Tee in AssertPrints and AssertNotPrints

Fixes a test failure caused by the Tee object being lazily closed only
when an AssertPrints/AssertNotPrints object is garbage collected.
Merge pull request #6429 from quantopian/transformer-rejection

Make it possible for AST transformers to reject input.
Fix typo
Simplify test_ident using str.isidentifier()

I have checked that this gives the same results as the previous method.
Remove leftover debugging
Merge pull request #19 from takluyver/latex-complete-fixes

Latex completion fixes
Add docstring for latex_matches method