Problems with bytecode encoding

[pfalcon]

1. Description is sparse/not clear.
2. qstr and constant encoding per code block (== function). Instead, should be per module to allow better reuse. - .mpy ver 4 provides way to achieve that for qstr's (TBC)
3. "code info" is mis-nomer. It has both length encoded and also ends with 0? - kinda fixed in .mpy ver 5
4. function argname qstr's are stored in const_table and waste some space there (given that qstr's a 2-byte encoded, while entry in const_table is void*).