Number conversion buffer size

[gregjesl]

The string buffer currently used to convert numbers to strings is fixed:

simpleson/json.h

Line 72 in 35592ed

char cstr[NUMBER_TO_STRING_BUFFER_LENGTH];

Instead, the function should use the known maximum sizes of each type

[gregjesl]

snprintf can be used to see if the buffer was too small: https://www.cplusplus.com/reference/cstdio/snprintf/