Dev: Add JS date lib by Matt Kruse (javascripttoolbox.com)

@c-schmitz
I am desperately missing a JS function to parse a date string using a format identifier. In PHP no problem but in JS...

I would therefore like to add this small lib (or just one function of it) to LS but was unsure where and how to put it. Hence the pull request. I actually would like to make some minor modifications to it before merging so the format identifiers match those of LS and are most convenient to us.

Can I just modify this lib, put a note in the file that it's been modified and have this in third_party? Sorry if that seems a dumb question...still new to OSS and LS :)