Replaces download-test-fonts.sh with download-test-fonts.py
which does the same work, and also avoids downloading anything
if the files are already installed with the right content.
Now uses the first 8 byte of each file's sha256 hash for the
digest.
* tests/README.md: documentation explaining how to
build and run the tests with the Meson build.
* tests/scripts/download-test-fonts.sh: Simple script
to download test font files to the 'tests/data/'
folder.
* meson.build, meson_options.txt, tests/meson.build:
Add 'tests' option to enable building and running the
test programs, disabled by default.
* tests/issue-1063/main.c: Simple regression test to
exhibit issue 1063.
* .gitignore: Ignore the content of the tests/data/
folder for now.
