Trusty has gtk-doc 1.20 which has better markdown support which should
fix some of the brokenness in the newly added documentation. The build
seems to be as fast as the current container-based build on Precise.

Fixes failures in others' forks, like:
https://travis-ci.org/khaledhosny/harfbuzz/jobs/99719710#L3912

[docs] More buffers documentation

More docs

Remove unused HB_SHAPER_DATA_ENSURE_DECLARE lines.

The coretext_aat shaper delegates to the regular coretext_..._ensure() functions, so coretext_aat_..._ensure() functions defined by these macros are unused. The compiler warns about them, which in turn can confuse people to think that the coretext_aat_..._ensure() functions weren't called by accident.

Now it is just reporting one error about “503 undocumented or incomplete
symbols”, that will be the easy part I guess.

Remove unused `retry:` label.

Temporarily makes it rebuild docs on every change again.

Doc fixes

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

To lower the number of gtk-doc warnings.

Fixes a -Wunused-label warning when building harfbuzz with clang -Wall.

Otherwise, almost all API functions are not extracted.

Lets see if it works…

I've set up a secure var for behdad/harfbuzz through Travis web interface, no need
to set the var here.

Deploy docs to gh-pages branch from Travis builds

This test font had a upem of 769, which results in rounding-related errors with
the FreeType font funcs.  Change the upem to 1024 to fix that.

Fixes https://github.com/behdad/harfbuzz/issues/201

Use chapter ids instead of numbers, so that we can reorder them,
introduce new ones etc. without the numbers becoming out of date.

Build docs in Travis and push them to the gh-pages branch, which makes
them available at http://behdad.github.io/harfbuzz/

Apparently class=0 is used for ClassDef1.  See:
https://github.com/adobe-type-tools/afdko/issues/90

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.

We regeressed Malayalam in 508cc3d3
This brings down the failures to 198 (from 750).

BENGALI: 353725 out of 354188 tests passed. 463 failed (0.130722%)
DEVANAGARI: 707307 out of 707394 tests passed. 87 failed (0.0122987%)
GUJARATI: 366349 out of 366457 tests passed. 108 failed (0.0294714%)
GURMUKHI: 60732 out of 60747 tests passed. 15 failed (0.0246926%)
KANNADA: 951190 out of 951913 tests passed. 723 failed (0.0759523%)
KHMER: 299070 out of 299124 tests passed. 54 failed (0.0180527%)
MALAYALAM: 1048136 out of 1048334 tests passed. 198 failed (0.0188871%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271662 out of 271847 tests passed. 185 failed (0.068053%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)
MYANMAR: 1123865 out of 1123883 tests passed. 18 failed (0.00160159%)

Test stats remain unchanged, except for Malayalam, which we investigate:

BENGALI: 353725 out of 354188 tests passed. 463 failed (0.130722%)
DEVANAGARI: 707307 out of 707394 tests passed. 87 failed (0.0122987%)
GUJARATI: 366349 out of 366457 tests passed. 108 failed (0.0294714%)
GURMUKHI: 60732 out of 60747 tests passed. 15 failed (0.0246926%)
KANNADA: 951190 out of 951913 tests passed. 723 failed (0.0759523%)
KHMER: 299070 out of 299124 tests passed. 54 failed (0.0180527%)
MALAYALAM: 1047584 out of 1048334 tests passed. 750 failed (0.0715421%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271662 out of 271847 tests passed. 185 failed (0.068053%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)

Myanmar, compared to Windows 10 mmrtext.ttf:

MYANMAR: 1123865 out of 1123883 tests passed. 18 failed (0.00160159%)

The DEFAULT naming wasn't helpful, so just remove it.