bundle2: add some distinction between mandatory and advisory part Mandatory part cannot be ignored when unknown. We raise a simple KeyError exception when this happen. This is very early version of this logic, see inline comment for future improvement lead.

bundle2: introduce a `parthandler` decorator Simple syntax sugar to register an handler for a new part type.

bundle2: first version of a bundle processing We now have a function that interpret part content. This is a version early version of this function. It'll see major changes in scope and API in future development. As for previous I'm just focussing on getting minimal logic setup. Refining will happen with real world usage.

bundle2: rename unbundle2 test command to statbundle2 We will introduce object to actually process the bundle, we need to keep the simplistic unbundle around for the test.

bundle2: safely read unpack data from part header We use the same approach that the other unpack, as function is given the struct format and his both responsible for reading the right amount of data from the header and unpack the struct. This give use flexibility if we decide to change the size of something in the format before the release.

transaction: drop extra import caught by pyflakes