v0.0.3

First cut of multiplexed files support, where you can read/write structs of different types to and from the same file. A discriminator field and record length is prepended to each record.

Fields whose names begin with underscore are now considered hidden/reserved fields. They can be use to add padding and force specific alignments.

Improve the error messages in the tokenization stage.

Numerous improvements to the C and python code. Added support for new types: bytearray, stringlist, intstack.