This is a fork of the flt2dec portion of rust-strconv [1] with
a necessary relicensing (the original code was licensed CC0-1.0).
Each module is accompanied with large unit tests, integrated
in this commit as coretest::num::flt2dec. This module is added
in order to replace the existing core::fmt::float method.
The forked revision of rust-strconv is from 2015-04-20, with a commit ID
9adf6d3571c6764a6f240a740c823024f70dc1c7.
[1] https://github.com/lifthrasiir/rust-strconv/
c82da7a54b