Relented on the strict import of direct objects/classes for the typing
module only. Typing module components can be directly imported because
it makes the code really painful to read and write otherwise.
This is still in-line with the python style guide adopted from Google at
http://google.github.io/styleguide/pyguide.html section 2.2.
Layers now accept metadata dictionaries (and chain/stack them on top of
those from lower layers). Metadata can only be set at construction
time, and the metadata dictionary is readonly. The hope is this will
make enumerating metadata keys across the codebase simpler.
The current metadata items that layers hold is:
architecture (Unknown | Intel32 | Intel64)
os (Unknown | Windows | Linux)
pae (bool)
page_map_offset (int)
This patchset may develop further to help enumerate all of these
(through a registration/reporting system).
Mike Auty