Add python script for building tarballs.

* scripts/ New file.

This standalone Python script should be equivalent to running `make
dist` with the Make-based build system, with the following minor

- Since `make distclean` doesn't always clean up `objs/` properly,
  `make dist` archives may contain some stale binaries like
  `objs/.libs/` or others.

- `config.guess` and `config.sub` are not updated unless option
  `--gnu-config-dir=DIR` is used to specify the location of these

- Some bits of the auto-generated reference documentation may
  appear in slightly different order, probably due to issues related
  to mkdocs and docwriter.

As an example, the call

  scripts/ /tmp/freetype2-dist

creates the following files under `/tmp/freetype2-dist`:

2 files changed