Close issue #587 properly escape shell iPython magic that begins with special characters.

[Skylion007]

This solves the issue of trying to run an executable script in the current directory, reference an absolute path to an executable or reference an environmental variable with iPython magic.

Previously, '!' iPython magic was not properly commented / uncommented for more complex Bash iPython magic constructions.

I've added tests to cover these more complex changes and modified the appropriate regex to handle the most common special characters.

Fixes #587

[lgtm-com]

This pull request introduces 2 alerts when merging e6caf08 into 213acee - view on LGTM.com

new alerts:

• 2 for Wrong name for an argument in a call

[Skylion007]

@mwouts the lgtm alert is outside of the code I edited in my PR

[lgtm-com]

This pull request introduces 2 alerts when merging 57c0a69 into 213acee - view on LGTM.com

new alerts:

• 2 for Wrong name for an argument in a call

[mwouts]

Awesome! Thank you @Skylion007.
Indeed the issue raised by LGTM is not related to your contribution.
Let me see if I can fix that one first at #589 - I'll come back here afterwards.