See previous commit.

The font Garamond Premier Pro Caption (and possibly many other
Adobe fonts), have many FeatureParamsSize tables with the old
wrong offset.  We handle fixing those up, but they were still
contributing to edit_count, and when I reduced HB_SANITIZE_MAX_EDIT
from 100 to 8 in 14c2de32, these
fonts were now getting GPOS dropped and hence kerning disabled.

Fix, by not counting edits made towareds offset fix-up.  I'll
also increase edit count again, in the next commit.

[travis] Try building on Trusty

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 without the numbers becoming out of date.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.