Allow converting from now steam ids to steamid64 and old steam ids

[icewind1991]

[babofitos]

Thanks for your contribution. There's some changes I'd like before merging. Can you take off the semicolons at the end of each line to keep consistent with the rest of the code? Can you use bignumber in lieu of lines 69 + 70? v.plus(parseInt(parts[1], 10)).toPrecision(17) should work since parts[0] will always be 1 and never 0.