bake: Enable multiprocess baking. Baking is now done by running a worker per CPU, and sending jobs to them. This changes several things across the codebase: * Ability to not cache things related to pages other than the 'main' page (i.e. the page at the bottom of the execution stack). * Decouple the baking process from the bake records, so only the main process keeps track (and modifies) the bake record. * Remove the need for 'batch page getters' and loading a page directly from the page factories. There are various smaller changes too included here, including support for scope performance timers that are saved with the bake record and can be printed out to the console. Yes I got carried away. For testing, the in-memory 'mock' file-system doesn't work anymore, since we're spawning processes, so this is replaced by a 'tmpfs' file-system which is saved in temporary files on disk and deleted after tests have run.

CHANGELOG
=========

This is the changelog for PieCrust.

The first section deals with the latest changes in the development branch
(``default`` in Mercurial, ``master`` in Git).

The second section deals with changes in the stable branch (``stable`` in
Mercurial, ``git-stable`` in Git), but those changes are also included in the
development branch (the development branch is ahead of the stable branch).


Fresh changes
-------------

*None... this stuff is still being prepared...*

Frozen changes
--------------

*None... this stuff is still being prepared...*