Add support for C99 types

Created by: shreyasbharath

Hi again,

At the moment, the library only supports a single non-portable unsigned type (long) and double.

long time          = root["time"];
jsonObject["time" = (long)time;   // If time is a uint32_t

Would it be possible to add support for C99 types (e.g. uint8_t, uint16_t, uint32_t, int8_t and float etc.) for accessing and setting JSON values? This would get rid of a lot of unnecessary casts in codebases that use C99 types like ours.

uint32_t time          = root["time"];
jsonObject["time"]  = time;

Thanks!