internal: Code reorganization to put less stuff in `sources.base`. Interfaces that sources can implement are in `sources.interfaces`. The default page source is in `sources.default`. The `SimplePageSource` is gone since most subclasses only wanted to do *some* stuff the same, but *lots* of stuff slightly different. I may have to revisit the code to extract exactly the code that's in common.

@echo off
setlocal

set CUR_DIR=%~dp0
set CHEF=%CUR_DIR%..\bin\chef
set OUT_DIR=%CUR_DIR%..\piecrust\resources\messages
set ROOT_DIR=%CUR_DIR%messages

%CHEF% --root=%ROOT_DIR% bake -o %OUT_DIR%
del %OUT_DIR%\index.html