The size was calculated based on wire type. We need to calculate based on
field type because for sint32/sint64 we need to zigzag encode the value
before calculating the size of varint.

- littleEndia32/64 arguments were in wrong order in a few places
- add safeReadStr that throws and exception if couldn't read enough data
- throw exceptions when not reading enough data

We have distinct procs for reading and writing differently encoded data, so
we don't need distinct types in this case.