Document RawDecoder functions - make a few functions protected.
Document RawDecoder functions - make a few functions protected.

anarsoul/rawspeed,anarsoul/rawspeed,anarsoul/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,klauspost/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,mgehre/rawspeed,LebedevRI/rawspeed,klauspost/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,mgehre/rawspeed,LebedevRI/rawspeed