API changes:
- If NDEBUG is defined, define HB_NDEBUG
- Disable costlier sanity checks if HB_NDEBUG is defined.

In 1.2.3 introduced some code to disable costly sanity checks if
NDEBUG is defined.  NDEBUG, however, disables all assert()s as
well.  With HB_NDEBUG, one can disable costlier checks but keep
assert()s.

I'll probably add a way to define HB_NDEBUG automatically in
release tarballs.  But for now, production systems that do NOT
define NDEBUG, are encouraged to define HB_NDEBUG for our build.

Saves some sweet time and binary size!

Fixes https://github.com/behdad/harfbuzz/issues/223

Right now we cannot test this because it has to be tested using hb-fuzzer.
We should move all fuzzing tests from test/shaping/tests/fuzzed.tests to
test/fuzzing/ and have its own test runner.  At that point, should add
test from this issue as well.

Some of it (create, reference, destroy) are adapted from Cairo docs.

Currently just announces lookup applications.  Message-API *will* change.
hb-shape / hb-view are updated to print-out messages to stder if --debug
is specified.

This reverts commit 68b507a3.

Commit abadc171 provides a better
fix for this.

https://github.com/behdad/harfbuzz/issues/161

See discussion here:
https://github.com/behdad/harfbuzz/commit/81ef4f407d9c7bd98cf62cef951dc538b13442eb

There's no way to disable this fallback, but I don't think it would
be needed.  Let's hope for the best!

Fixes https://github.com/behdad/harfbuzz/issues/153

Fixes https://github.com/behdad/harfbuzz/issues/103

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=541608
and cluster test.

Needed for upcoming merge-clusters fix.

TODO: Documentation.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=71445

Fixes test-shape, and:
https://code.google.com/p/chromium/issues/detail?id=497578

Based on data from http://upstream-tracker.org/versions/harfbuzz.html
Resolves #103

Annotate the output parameter.

It should not be freed by the caller.

Fixes coretext notdef loop consisting of all default_ignorable glyphs

https://code.google.com/p/chromium/issues/detail?id=464755

In hb-coretext, when we were using scratch buffer for book-keeping,
a reverse_range() caused by the notdef-insertion loop could mess up
our log_clusters.  Ouch!

This is by no ways to promote non-Unicode encodings.  This is an entry
point that takes Unicode codepoints that happen to all be the first
256 characters and hence fit in 8bit strings.  This is useful eg in Chrome
where strings that can fit in 8bit are implemented that way, and this
avoids copying into UTF-8 or UTF-16.

Perhaps we should rename this to hb_buffer_add_codepoints8().  I'm also
curious if anyone would be really interested in hb_buffer_add_codepoints16().

Please discuss!

Minimal shaping works now!

After 763e5466, one doesn't
need to set flags for different pieces of text.  The flags now
are something the client sets up once, depending on how it
actually uses the buffer.  As such, don't clear it in
clear_contents().

Tests updated.

With this change, we now by default replace broken UTF-8/16/32 bits
with U+FFFD.  This can be changed by calling new API on the buffer.
Previously the replacement value used to be (hb_codepoint_t)-1.

Note that hb_buffer_clear_contents() does NOT reset the replacement
character.

See discussion here:

https://github.com/behdad/harfbuzz/commit/6f13b6d62daae4989e3cc2fe4b168e5c59650964

New API:

  hb_buffer_set_replacement_codepoint()
  hb_buffer_get_replacement_codepoint()

Like hb_buffer_add_utf32, but doesn't do any Unicode validation.
This is like what hb_buffer_add_utf32 used to be until a couple
commits ago.

Disables any cluster-merging.  Added for testing purposes while
we investigate what kind of API to add for this.

Previously we were only setting this in hb_buffer_clear_contents(),
but set_length(0) is a valid way to reinitialize buffer to use with
new text.

Fixes last of scratch alignment warnings in hb-coretext.

Commit 6b65a76b.  "end" was becoming
negative.  Was trigerred by Lohit-Kannada 2.5.3 and the sequence:
U+0CB0,U+200D,U+0CBE,U+0CB7,U+0CCD,U+0C9F,U+0CCD,U+0CB0,U+0C97,U+0CB3
Two glyphs were being duplicated.

Previously we only supported recursive sublookups with
ascending indices.  We were also not correctly handling
non-1-to-1 recursed lookups.

Fix all that!

Fixes the three tests in test/shaping/tests/context-matching.tests,
which were derived from NotoSansBengali and NotoSansDevanagari
among others.