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.

Allows accepting uniXXXX format.

Fixes https://code.google.com/p/chromium/issues/detail?id=476913

This reverts commit 89cbd4d9.

See discussion:
https://bugzilla.gnome.org/show_bug.cgi?id=747772

Improve hb-shape/hb-view's help text w.r.t. output options 

Not sure we have any right now; motivated by this:
https://bugzilla.gnome.org/show_bug.cgi?id=747772

More ntrospection fixes

Annotate the output parameter.

Fix build on WEC2013

It should not be freed by the caller.

Based on patch from Björn Breitmeyer

This is a tool that lists all fonts that can render a given string.
It uses hb_shape() to do so, and as such is aware of HarfBuzz's
normalizer.

Previously, when creating an object from inert inputs (eg:
"hb_font_create(hb_face_get_empty())") we returned the inert
empty object.  This is not helpful as there are legitimate
usecases to do that.

We now never return the inert object unless allocation failed.

Tests are revised to reflect.

Applies to --font-size and --margin.

Hopefully the scanf usage here doesn't have compatibility issues
(star being counted in the return value, etc).