Parse angle in styles as double number

Similar to VSFilter. Thanks to Iroha for reporting this issue.

Note: this breaks the ABI!
Fix fallback event formats

Fixes issue 83.
Add Blur field to ASS_Style

Useful when applications specify the style manually for non-ASS
subtitles.
Scale border size with user font size coefficient
Make closing ')' optional for some ASS tags

It appears VSFilter generally accepts the tag anyway if closing ')' are
missing in tags like \pos(1,2). Since they're not strictly needed
anyway, make the last ')' optional in order to make parsing more
tolerant against broken subs.

Fixes issue #79.
Add ass_set_storage_size and fix related scaling issues

\blur radius is not scaled from script to storage resolution
but is scaled from storage to display resolution. The same
applies to borders and shadows if ScaledBorderAndShadow is "no".
(If it is "yes", borders and shadows are scaled from script
to display resolution just like before.)
Support reading the YCbCr Matrix header

The value is parsed and stored as an enum constant that the consumer
can read from ASS_Track. All output images are still plain RGB,
and the consumer is expected to perform its own color correction.

Supported header values: (TV|PC).(601|709|240M|FCC) and None.
If the header is missing, a special compatibility value is used
that should be treated as TV.601 if the accompanying video stream
is YCbCr and as None otherwise. If the header is present but has
an invalid/unknown value, a different special value is substituted.
shaper: correctly handle @font advance

The code was confusing glyph index and unicode codepoint index.

Fixes issue 94.
shaper: proper script/language handling

Determine script for each character and use this as an additional
property for splitting up the text into runs. Characters of Common
or Inherited script assume the script of the preceding character. If
that is not possible (First character(s) in a run are Common/Inherited,
for instance), a backwards scan is done so they can assume the script
of the following character.

Additionally, determine default language in case no override is
set. This simply maps a language to a script, if a language exists
that is mostly representative for a given script. Pango's mapping
has been adapted.

This helps with fonts that don't have OpenType features set up
for default script/language pairs. It's also considered to be right
approach by most people, and might help with correct OpenType rendering
in some other cases.

Fixes issue 85.
Add type field to ASS_Image struct

Patch by chrisburel, posted on Google code issue 31.
Fix crazy VSFilter behavior for \move tag

Fixes issue 90 (both cases).
Don't overwrite user-defined aspect ratio settings

ass_set_storage_size() overwrote the user-defined aspect ratio set with
ass_set_aspect_ratio(). Change it so that if ass_set_aspect_ratio() is
used, the ass_set_storage_size() parameters are not used for any aspect
ratio calculations. (The storage size is still used for calculating the
blur scale.) This simplifies the code as well, because the aspect ratio
is now centrally calculated in ass_start_frame().

Update the doxygen. Make it clear that ass_set_storage_size() will be
used for aspect ratio calculation, unless ass_set_aspect_ratio() is
used. Also mention what libass actually does with the dar and sar
parameters: it uses them to calculate a pixel aspect ratio, nothing
else.

Explicitly allow resetting the storage size with w=h=0. Document that
it's allowed to remove the user defined aspect ratio by setting a pixel
aspedct ratio of 0.

See issue 6.
Add ass_set_pixel_aspect(), deprecate ass_set_aspect_ratio()

ass_set_aspect_ratio() is confusing, because it takes a DAR and SAR
value, while libass just needs a single pixel aspect ratio. Introduce
ass_set_pixel_aspect(), which sets the pixel aspect ratio directly.

ass_set_aspect_ratio() is considered deprecated. There's no reason to
remove it, but hopefully directing users to ass_set_pixel_aspect() will
make for a simpler API.

Improve the doxygen and document what ass_set_margins() actually does.
Ignore junk in nested \t tags

Normally, junk between tags is ignored. But unlike vsfilter, libass
doesn't do that inside \t tags. So the following fails and will never
actually switch the color: {\t(1000,1000,(\c&HFF0000&))} (The '(' and
')' are junk, and are not covered by any ASS documentation.)

Instead expecting that the last parameter to \t (the parameter that
takes nested tags) starts with '\', turn it around and assume that the
first parameter that's not a number is the last parameter. (This
parsing is kind of awkward because we don't do any lookahead.)
Likewise, let the nested tag parsing terminate on ')' instead of
checking whether a tag is started with '\'. This allows skipping
junk in the middle of the nested tag, without terminating too early.
(Check '}' and '\0' in case the tag is not properly terminated.)
Bump LIBASS_VERSION

The ABI was broken and a new API function were introduced.
Clip tag arguments are not optional

This fixes: {\clip(1,1,20,20)\clip\alpha&H1E&\c&HC7E5C0&}X

libass tries to interpret the second \clip, which has no arguments.
Since the parsing code doesn't require a starting '(', the parser will
skip over the other tags (treating them as junk) and interpret the
numbers that happen to be in the rest of the string. The result is a
bogus drawing command, which happens to rasterize an extremely wide
glyph, which takes several seconds to finish.

Make the '('  required. Neither the aegisub manual nor the vsfilter
source code have any indication that \clip without starting '(' is
allowed, so this should not break anything.
fontconfig: remove default "lang" setting from patterns

Fontconfig defaults set the "lang" value in patterns, and it then
prefers fonts which are listed as supporting this language. The
default value may not match actual script language, and even a setting
of "en" for English subtitle can cause problems. Remove the "lang"
setting from patterns used to find fonts.

A file had a normal and an oblique version of the same font attached,
with different character set coverage: the normal version lacked some
non-ascii characters that fontconfig includes in its list of
characters required for English support. As a result, the oblique
version was picked for what was supposed to be normal text.
Allow building as DLL on Windows

Patch by jon_y on IRC.
Improve font mismatch message

Example for an old message:

 [ass] fontconfig: Selected font is not the requested one: 'DejaVu Sans' != 'Wingdings'

it was hard to tell which was the selected and the requested font.
Also, it's not really clear what's the problem at all. Why would it
select a different font? Obviously, the issue is that it can't find
the font in the first place.

Now it prints:

 [ass] fontconfig: cannot find glyph U+006C in font 'Wingdings', falling back to 'DejaVu Sans'

Or if the code parameter for select_font() is 0:

 [ass] fontconfig: cannot find font 'Wingdings', falling back to 'DejaVu Sans'

I'm not sure if this message is really accurate in all cases. It's
possible that there are more reasons for failure. But all things
considered, this should be easier to understand.
Fix blur scaling

Commit 0e1702ad7a6a827d "Add ass_set_storage_size and fix related scaling issues"
attempted to fix blur scaling. This breaks blur scaling for players
which don't call ass_set_storage_size().

This commit reverts the default behavior to the old behavior. The
behavior when ass_set_storage_size() is called should be unchanged.