Stdlib: Need a way to parse a string into a number

[phated]

Day 2 of Advent of Code has you parsing a string like:

1-3 a: abcde
1-3 b: cdefg
2-9 c: ccccccccc

Into a ruleset to match, with the numbers being a min-max range. I'm going to implement this as a constant pattern match right now, but we should have a way to parse a string into a number.

[phated]

@ospencer do we want to close this now that parseInt was added or do we want to leave open until we have parseNumber?

[ospencer]

I think we can close once parseFloat lands.