Rationale: it's easy to implement the callback wrong. Doing so introduces
io errors when unknown fields are present in the input. If code is not
tested with unknown fields, these bugs can remain hidden for long time.
Added a special case for the memory buffer stream, where it gives a small
speed benefit.
Added testcase for skipping fields with test_decode2 implementation.
Update issue 37
Status: FixedInGit
Replaced the confusing pb_enc_* functions with new pb_encode_* functions that
have a cleaner interface. Updated documentation.
Got rid of the endian_copy stuff in pb_encode.c, instead using C casts to do it automatically.
This makes the code safer and also reduces binary size by about 5%.
Fixes Issue 6.
