Handle patterns containing {, }, [, ] and \ characters

[shreepads]

Allow the chars {, }, [, ] and \ to be used within a given "[xyz]" pattern 'escaped' with the "" char.

So, for example to use the "[" char in a given pattern use:
[abc[xyz]

This will match to one of the following chars - a, b, c, , x, y and z

This issue is related to Issue #3 - unless this is fixed the :punct: character class won't work.

[shreepads]

To be handled in branch regexclass along with Issue #3

[shreepads]

Issue #3 has been closed without fixing this (and merged into baseopenmp) as this is a lower priority.

:punct: char class has been implemented without support for these chars.