define a codec table format

[wanderer]

This is the first attempt creating a format for defining codec tables. Codec tables map single bytes to multiple bytes in this case ascii strings which represent a multicodec prefix.

Table definition

Field	Type	Description
count	varuint32	count of type entries to follow
entries	type_entry*	repeated type entries as described below

Entry definition

Field	Type	Description
count	varuint32	the length of the string of a multicodec prefix
prefix	bytes	the prefix string
packed encoding	byte	The packed encoding of prefix

This is effectively layer 0 compression. Which is a simple binary encoding of the prefix bytes and related data structures. The encoding is dense and trivial to interact with.