Make sure alias templates are sorted according to distro aliases
ordering in config file as intended.

Previously, alias templates got sorted lexicographically.

Fixes: #93

Fixes: #63

Add 2 new config options to control special files in templates using
unix-style file name patterns:

* templates.ignore_files to ignore/skip files entirely
* templates.plain_copy_files to copy files without rendering

Docs and tests are included.

Fixes: #58

Support Jinja include directive:

    {% include 'distro/common/foo' %}

Paths are relative to project root.

A simple project demonstrating apkg templating features.