Add to apio.ini an option to control what files are included in the project

[zapta]

The goal is to allow different apio.ini envs to use different files, for example different module implementations.

Proposal: have a new apio.ini option called project-files whose values are a list of include: and exclude: glob patters.

project-files =
   exclude: lib/boards/*
   include: lib/boards/board1

For a given project file, the evaluation if the file is included or excluded from the env is done as follows

1. Initially the file is considered included.
2. The glob patterns are iterated in the order they are defined
3. If a file matches an include: (exclude:) directive its status is force to 'included' (excluded).
4. At the end of the end of iterating the patterns, the last file status wins.

These rules will not apply to apio.ini which must be unique and is always included.