Fix for documentation for RC_CHANNELS_OVERRIDE. See Github issue #72.
Replaced all occurances of 32767 & 65535 with INT16_MAX and UINT16_MAX. This makes it more clear that these aren't magic numbers. Additionally implies that the macros INT16_MAX/UINT16_MAX are to be used, which should be available in stdint.h.
Merge pull request #124 from Susurrus/override_fix

Override fix