[Structure] Add regular expressions

[geekygirlsarah]

Description

This issue is for adding a new structure for all languages that will let you compare a new aspect of a language. Ideally someone with many programming languages will help work on this.

This structure should show how to work with regular expressions. This could be:

• Are regular expressions their own object or just a fancy form of a string?
• How do you define the pattern?
• How do you run the search of the pattern?
• What types of objects can you run the search on? (Just strings? arrays of strings? Other things?)
• How do you retrieve multiple matches if searching in groups?
• Are matches returned lazily or greedily?
• What pattern standards are used (like POSIX BRE, POSIX ERE, POSIX SRE, Perl, etc.)

Or other things. It should take some thought on all of the features that any programming language could have. Upon making this PR, expect it to have some revisions as people from various programming language backgrounds offer suggestions.

Requirements

Decide if you want to make this its own file or a part of the pre-existing strings structure file. If it's fairly large, it should probably be its own file. If it's fairly small, it could maybe go with strings.

1. Look over the documentation at https://docs.codethesaur.us/thesaurus/add-new-structure/
2. Add a new file under web/thesauruses/_meta named whatever feels appropriate
3. Open up web/thesauruses/meta_info.json and add your new file to that file in the structures section.
4. Add in some categories, then add in the concepts under that
5. Feel free to use any _meta file as examples for how to do it
6. Make a PR and we can help test and review it