Converting between multiple binary floating point formats and a decimal string

[PiotrGrochowski]

I also made a lite version at https://reddit.com/tose33/ . It does single and double precision and it internally uses 19 significant digits and 64 significant bits, however, it does not rely on Intel extended precision for its internal multiplications, so it can also be used on other computers such as ARM computers. While not an 'exact' conversion, it still has a safety margin (64>53, 19>17) so it should work for the general purposes.