tweak test failure output. write to a temp file not stdout. test still fails because expected is not just an identical copy of input

Add basic directory structure for subsetter integration tests. Plus a utility for generating expected output files.

Fixes https://github.com/harfbuzz/harfbuzz/issues/741

Fixes MORX-21.

Fixes MORX-18, MORX-19, and MORX-22.

Correctly show if building documentation is enabled or not in configure
summary.

Fixes https://github.com/harfbuzz/harfbuzz/issues/741

The atexit() man page indicates that this is expected to behave
in the expected way on unloading of shared libraries.

If the `calloc` for `gsub_accels` or `gpos_accels` fails, then the
unlikely branch afterwards can be taken, which frees up the
`hb_ot_layout_t`, but since those fields can now be `nullptr`, then
we don't want to dereference them.

In `reference_table`, if the data is empty and we return early,
we still need to release the data object.

In `hb_coretext_shape`, there two edge cases where an early
return should release the attributed string.

Remove the faulty loop-detection logic. Use max-ops for breaking
out of infinite loops or heavy work.

https://twitter.com/behdadesfahbod/status/958065026262183936

Fixes https://github.com/harfbuzz/harfbuzz/issues/712

Issue originally reported at http://cppfiles.com/chromium.txt .

This fixes what appears to be a copy - paste issue which causes both
KernSubTableFormat2::rightClassTable and the 'right' argument to
KernSubTableFormat2::get_kerning to go unused.