Python v3 migrating.

Fixed python realization of mavlink protocol
Added array containing all encoding C functions

Manual writing of switch-case decoding routine for every new project is
annoying me. So I aggregated all decoding functions in array of
function pointers. Now I just call function using msg_id as array index.
I know about code size increasing but:
1) this is optional feature
2) FLASH size in MCUs now cheap resource (in opposite to RAM)
Merge branch 'encode_table' of github.com:barthess/mavlink into encode_table