stb_truetype: fix incorrect antialiasing computation in v2 rasterizer, and handle certain cases where math blew up

No actual bugs as far as I can tell.

Fixes issue #1162.

Fixes issue #979.

To pacify GCC warnings at -Wimplicit-fallthrough=4. Why the
all-caps version works and the others don't, I'm not sure; the
GCC manual page lists regular expressions that GCC is checking for
but does not say which regular expression syntax variant it's using,
whether it's looking for a substring match or a full match for
the comment, and what exactly the text being matched against is
for a single-line comment. Sigh.

Fixes issue #507.

Was using 4-character spaces and otherwise formatted unlike the
rest of the code, fix this. Also get rid of the outer switch in
GetGlyphGPOSInfoAdvance with just one case; just use an if.
No behavioral changes.

Glyphs not assigned a glyph class should default to class 0 as
per the OpenType spec. Also, change the code to treat malformed
data as an error to be handled, not an assert, and change the
way the version checking works.

Fixes the issue mentioned in PR #1035. Also, this part of the
code is indented incorrectly; will fix that in a subsequent
commit.

GCC warns about a potentially uninitialized variable here. It's
not (or at least I don't see how), but fix it anyway.

Confirmed from the OpenType spec that there's nothing missing
here. (These were just annotations listing the total sizes of
the tables, but this is not used for anything here.)

Fixes issue #704.

Whitespace only.

Fixes the bug covered by PR #1066, but with a slightly different
fix that's hopefully a bit clearer.

Fixes the bug covered by PR #1066, but with a slightly different
fix that's hopefully a bit clearer.

While it is recommended that the numberOfContours are set to -1 for compound glyphs, it is allowed to have any negative value. Source: https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6glyf.html

However, I don't know if this happens in practice.

The fucntions are:
stbtt_GetCodepointSVG - provides a pointer to the SVG data in the supplied argument, and returns the length of this data
stbtt_GetGlyphSVG - As above but takes the glyph index instead of the codepoint
Note that the returned data may be deflate compressed.

When calling stbtt_PackFontRanges, multiple missing glyphs in the range
of codepoints will create multiple copies of the font's missing glyph to
be added to the pixel buffer.  Instead, the first codepoint that maps to the missing glyph will add it to the pixel buffer, and all subsequent glyphs will simply copy the stbtt_packedchar data to reference the same region of the buffer.

This does NOT prevent duplication in multiple calls to stbtt_PackFontRange(s) - that would require modifying the packing context, which could be nice but is a bit more intrusive.

also fix a comment typo

Replace ASCII art with slightly crappier ASCII art that is not
going to make compilers complain about trailing backslashes.

Fixes issue #707.