Support multiline strings

[maxrothman]

Currently this extension is not capable of recognizing multiline quote-delimited strings. For example:

foo='asdf
asdf
asdf'
echo "$foo"

This is a valid bash script. If you place your cursor inside the string and triggering "Select inside either quote", nothing happens.

Multiline strings like this are common in many languages, it would be nice for this extension to support them.