Add ability to specify infinity and NaN strings

[planet36]

It would be nice if a user could specify the string representation of infinity and NaN values.

For example:

• "nan" instead of "NaN"
• "inf" instead of "Infinity"

[ulfjack]

I generally agree, but I haven't found a nice way to do that.

[Snuggan]

Would something like this work?
#if !defined(RYU_MEMCOPY_NAN)
#define RYU_MEMCOPY_NAN int memcpy_nan( char * dest_) { memcpy( dest_, "nan", 3 ); return 3; }
#endif
RYU_MEMCOPY_NAN

#if !defined(RYU_MEMCOPY_INF)
#define RYU_MEMCOPY_INF int memcpy_infinity( char * dest_) { memcpy( dest_, "Infinity", 8 ); return 8; }
#endif
RYU_MEMCOPY_INF

#if !defined(RYU_EXPONENT)
#define RYU_EXPONENT 'e'
#endif

...and use memcpy_nan/memcpy_infinity/RYU_EXPONENT where appropriate?