Format, update numtoa; Avoid panicking & allocating in event parsing

I'm not a fan of how the code to avoid allocations looks like, but I haven't found another way. I'm also not 100% sure that it is correct, but all the tests are passing, so that's a good sign.

Edit: The major reason that panicking in event parsing is bad, is that the enduser has to guarantee that a CSI sequence is complete, which they can't do without basically replicating the event parser.