Rewrite command-line splitting to tokenize quoted strings

[stecman]

This replaces the previous simple "split on breaks" regex in CompletionContext::splitCommand() with a function that behaves as a tokenizer and uses a more complete regex.

This adds support for completion of:

• Escaped spaces (and other characters): Some\ multi\ word\ sequence
• Quoted strings: "have some double quotes" / 'you\'ll get single quotes too'
• ~="" style options: --foo="bar"~ (couldn't repro this working)

To do:

• [x] Add support for output of quoted/escaped strings during completion. This first commit adds the input side only - a completion for a multi word string incorrectly results in multiple suggestions at the moment. Either need to keep state of which word indexes were quoted, or just automatically quote/escape all suggestions for shell output.

Resolves #67

[stecman]

Under BASH and ZSH this now looks like this:

Still needs a little tweaking to make BASH escape quotes inside completions, but otherwise should be ready. Feel free to test this.

[stecman]

@JoshuaBehrens, @aik099 this is ready to merge now if you want to test/review.

[JoshuaBehrens]

@stecman you are a man of honor. I will test as soon as possible. If it works out this change can be part of the almost dusty PR :+1:

[JoshuaBehrens]

Merge it and release a new version :+1: Very good work

I had no problems anymore with whitespace or special chars I am used to work with.

[JoshuaBehrens]

Thanks for creating a new minor version. Apparently packagist is not yet aware of it :disappointed:

[stecman]

Aha, the Packagist hook just needed updating - published now :+1: