Add string variation to all REs

[zanerock]

Overview

It's useful to have string versions for partial matches and embedding. Let's make a string version of each RE.

Deliverables

• add 'XXXREString' for each RE.
• update documentation

Additional changes

• add missing periods in the javascript RE documentation

[zanerock]

Work for this issue will begin begin on branch work-liquid-labs/regex-repo/27.