Added colon separated time support

[barinali]

This branch covers #24.

I don't know why @stuartpb closed his pull request, but I wanted to mention him anyway. Because I just refactored his code block a little bit and added some tests to cover the feature.

[stuartpb]

Worth noting that the closed pull request in question was #25, which was written to close #24

[stuartpb]

Okay, this was four years ago, so it's a bit of a challenge for me to remember back to when I wrote the PR, but if I remember correctly, the reason I closed it was because, on testing, the parsing failed because ms.js didn't actually handle mixed times (ie. it could handle 3h or 4m but not 3h4m). It's possible that's changed since the original PR, but from what I remember, that was the failure I experienced with the code submitted in #25.

[stuartpb]

Yeah, I'm pretty sure that's what it was - and, for that reason, this PR is busted, too: you're returning a rewritten string when given the parse input with a colon instead of a value in milliseconds (a rewritten string that, as the original issue still appears to be present in ms.js's implementation, would not parse to the correct time if you were to pass it back in to ms()).

[stuartpb]

The issue in question was raised in #54. A solution was proposed with #55 but never merged.

[rauchg]

Not a fan of this. Seems out of scope for ms

[rauchg]

Thank for the proposal!