Don't reset the readline completer after each prompt

This makes it impossible to setup a custom completer. The comment says that
"we must ensure that our completer is back in place," but I don't see why. All
that does it make it impossible to use a different completer. One can trick
IPython into not doing this by monkeypatching ip.has_readline to False, but
then certain features like multiline editing are no longer enabled.

See https://github.com/davidhalter/jedi/pull/321.
Use svg by default due to lack of Ghostscript by default on Windows
Add strip_url_static_file_prefix to filters
Add strip_url_static_file to base sphinx template and templateexporter.py
Add tests for filter
`strip_files_prefix` now also strips markdown style links, `latex_base` updated to include filter
Update IPython Pygments lexers.
Remove executable flag on __init__.py
Update code for making sphinx aware of IPython console lexer.
Add some discussion about new lexers.
Make IPyLexer available in Pygments as 'ipython' and 'ipython3'.
Skip doctests for IPythonConsoleLexer since they aren't doctests.
Update docstring for IPythonConsoleLexer.
Insert copyright again.
Updating some comments to reflect the actual code.
lexerself -> lexer.
More updates to comments and docstrings.
tweak formatter.for_type

- for_type(cls) nondestructively queries the current formatter (previously disallowed)
- for_type(cls, None) clears the current formatter (previously queried current)
exercise formatter.for_type in tests
Make 'matplotlib' optional when using the ipython directive.