Handle exponential floats

[zoryamba]

Hello.
Thanks for great library. It ensures good compression results on great performance.

Only issue i faced - compressing exponential numbers.
For integers with positive exponent it seems to work correct, but produces huge strings:

console.log(stringify(1e+123));
// ¢D6NHK4g4X000000000000000000000000000000000000000000000000000000000000

For negative exponent it produces wrong output:

console.log(stringify(1e-123));
// £0.0

I'll fix this and provide MR