TODO: Documentation.

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

Based on patch from Martin Hosken, with review from Jonathan and I.

Based on https://bugzilla.mozilla.org/show_bug.cgi?id=1183209

https://bugs.freedesktop.org/show_bug.cgi?id=91228

Commit cdcdfe61 changed two `#pragma
message` to `#pragma error` in hb-unicode.cc, however MSVC uses #error,
just like the #else branch. `#pragma error` is an unknown pragma so
MSVC does not fail the build because of it, which I believe was the
intention of that commit.

If it's meant to be an #error, then the #ifdef for _MSC_VER can be
removed entirely.

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

Separate the loops for the two cases of replacing with space
and deleting.  For deleting, use the out-buffer machinery.

Needed for upcoming cluster merge fix.

Based on test from https://code.google.com/p/chromium/issues/detail?id=497578

Currently fails.  Basically, if there's a default_ignorable at the
start of text, and font has no space glyph, we remove the default_ignorable,
and that makes the first char in text to correspond to no cluster.

Fix coming.

Until I figure out what to do about the API, and finalize
the tool.

Part of https://github.com/behdad/harfbuzz/issues/91

First try...

https://bugzilla.mozilla.org/show_bug.cgi?id=1167119

Fix "Since:" tags

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

Applying unary minus operator to unsigned int causes the following
warning on MSVS:

  warning C4146: unary minus operator applied to unsigned type, result still unsigned

Based on patch from Koji Ishi.

Fixes https://github.com/behdad/harfbuzz/pull/110

Using latest gobject-introspection, I don't seem to be having this
problem anymore:

  https://bugzilla.gnome.org/show_bug.cgi?id=707656

Removing that kludge makes language_t behave more like the way I expect it
in Python.

Also fixes:
https://github.com/behdad/harfbuzz/issues/91

Fixes user_data_t

Fix Travis CI config to pass again

Apparently the code is already standardized:
https://www.microsoft.com/typography/otspec/languagetags.htm

Add OpenType language tag 'NAV ' for Navajo.

Apparently the version on Travis is 1.32.0, while we require 1.34.0.

Very anaemic, needs to descripe the format understood by
hb_feature_from_string() etc., but it is just start.

The code is not standardized yet, but is used in some Google fonts.