Automatic matching of brackets and quotes

[mskar]

This PR

1. implements insertion and deletion of matched brackets and quotes
2. makes changes to ptpython/key_bindings.py
3. is similar to Update config.py to add auto close for brackets and parentheses #363, which only handles insertion (not deletion) and makes changes to config.py
4. shamelessly borrows code from randy3k/radian

Example:

1. Start ptpython
2. Press (, [, {, ', or " to insert a pair of round/square/curly brackets or single/double quotes with the cursor inside
3. Press backspace or ctrl h to delete the inserted bracket or quote pair

To install to version of ptpython in this pull request, run
python -m pip install git+https://github.com/mskar/ptpython.git@auto_match