The problem with HB_TAG_STR() was that it expected a string of size 4
exactly, and unlike hb_tag_from_string() it doesn't pad the tag with
space characters.  So, the new name is more appropriate.

Uses the glib testing framework.  Wrote unit tests for hb-common.h
types.

Never hurts.

Since we now assert thos in hb-private.h, the int types cannot be wrong.
(Except for when someone else includes hb-common.h in a very broken
configuration, but that's not our problem!)

Plus, we don't use inline in the public headers, so remove that too.

That better matches OpenType spec.  Note that we enable it for all
Arabic-shaper scripts.  Ie. we enable it by default for Syriac too,
but the SyriacOT spec does not require it.  I think this is a more
useful compromise than special-casing for Arabic script alone.

For now we don't use anything from the locale, but we should default
to using $LANG, etc, if --language is not specified.  Right?

The --features parsing handles errors now.  More importantly, it
allos limiting individual features to specific byte ranges.  The
format is Python-esque.  Here is how it all works:

  Syntax:	Value:	Start:	End:

Setting value:
  "kern"	1	0	∞	# Turn feature on
  "+kern"	1	0	∞	# Turn feature off
  "-kern"	0	0	∞	# Turn feature off
  "kern=0"	0	0	∞	# Turn feature off
  "kern=1"	1	0	∞	# Turn feature on
  "kern=2"	2	0	∞	# Choose 2nd alternate

Setting index:
  "kern[]"	1	0	∞	# Turn feature on
  "kern[:]"	1	0	∞	# Turn feature on
  "kern[5:]"	1	5	∞	# Turn feature on, partial
  "kern[:5]"	1	0	5	# Turn feature on, partial
  "kern[3:5]"	1	3	5	# Turn feature on, range
  "kern[3]"	1	3	3+1	# Turn feature on, single char

Mixing it all:

  "kern[3:5]=0"	1	3	5	# Turn feature off for range

Avoids recreating the face the second time we call draw().

Frees all allocated memory before exiting.  Useful for valgrind run.

Accepts values like:

  --features="-mkmk,aalt=2,calt=1,+cswh"

A minus sign means "=0", a plus sign means "=1".  Default is "=1".
A minus sign overrides an explicit value.

Also adds --script support to hb-view.

If a script tag is not known to us, we pass the ISO 15924 tag around.
Right now, the OT layer ignores that, but we can fix it to blindly
convert that to an OT script tag.

- Rename HB_SCRIPT_INVALID_CODE to HB_SCRIPT_INVALID

- Add HB_DIRECTION_INVALID

- Make hb_script_get_horizontal_direction() public

- Make hb_shape() guess script from buffer text (first non-common
  non-inherit script) if buffer script is set to HB_SCRIPT_INVALID (this
  is NOT the default.)

- Make hb_shape() guess direction from buffer script if buffer direction
is set to HB_DIRECTION_INVALID (this is NOT the default.)

- Make hb-view.c set INVALID script and direction on the buffer.

The above changes are meant to make hb-view fairly useful for uni-script
uni-direction text.  The guessing behavior however is NOT the default of
hb_shape() and must be asked for explicitly.  This is intended, because
the guess is not a suitable substitute to full-fledged bidi and script
segmentation.  It's just a testing tool.

Definitely not black!

Currently doesn't handle script or direction.

__LOC__ was renamed to _HB__LOC__ in cd7555 but the corresponding
change wasn't made in hb-private.h.

We just require people to have libtool, pkg-config, etc installed
when running autogen.sh

Reported on mailing list by Keith Stribley and Khaled Hosny.

We always allocate and grow str and pos together.

It was unmaintained and the code has to be replaced to use the new
grphite-ng code base.

Add support for classic Mongolian script to the Arabic shaper.

Still work to be done around U+180E MONGOLIAN VOWEL SEPARATOR as it
should not be included in the final glyph stream the same way that
ZWNJ, etc should not appear in the final glyph stream.

But the joining part should be done.

There remains the question of how should the U+18A9 MONGOLIAN LETTER ALI
GALI DAGALGA be handled as it has General Category NSM but a letter
nonetheless.  For now, our generic logic makes this a joining T instead
of joining D as other Mongolian letters are.

We added Mandaic joining data to the Arabic shaper a while ago, but
were not actually using the Arabic shaper for Mandaic.  Fixed.

Fix apply_lookup() for zero-input broken fonts.