Decimal string to floating point conversion with correct half-to-even rounding

[9il]

On Monday, 22 June 2020 at 10:53:02 UTC, Dukc wrote:
> On Sunday, 21 June 2020 at 15:24:14 UTC, 9il wrote:
> Can mir_parse handle other bases than decimal?

No, only the decimal basis is supported for now. Support for 
hexadecimal FP/integer parsing can be added though.

The basic stuff for correct FP hexadecimal parsing is done: we 
can convert a big integer view to FP number with half-to-even 
rounding.

So the algorithm would look like:
1. Parse hexadecimal big integer
2. Parse exponent
3. Cast big integer to `Fp` with a specific number of meaningful 
bits (its already implemented)
4. Add exponent to `Fp`'s exponent, and cast the result to a 
hardware floating point type.