[autofit] Introduce neutral blue zones to the latin module.

Such blue zones match either the top or the bottom of a contour.  We
need them for scripts where accent-like elements directly touch the
base character (for example, some vowel signs in Devanagari, cf.
U+0913 or U+0914).

* src/autofit/afblue.hin (AF_BLUE_PROPERTY_LATIN_NEUTRAL): New
property.

* src/autofit/afblue.h: Regenerated.

* src/autofit/aflatin.h (AF_LATIN_IS_NEUTRAL_BLUE): New macro.
(AF_LATIN_BLUE_NEUTRAL): New enumeration value.

* src/autofit/aflatin.c (af_latin_metrics_init_blues,
af_latin_hints_compute_blue_edges): Handle neutral blue zones.
[autofit] Fix handling of neutral blue zones in stems.

* src/autofit/afhints.h (AF_Edge_Flags): New value
`AF_EDGE_NEUTRAL'.

* src/autofit/aflatin.c (af_latin_hints_compute_blue_edges): Trace
neutral blue zones with AF_EDGE_NEUTRAL.
(af_latin_hint_edges): Skip neutral blue zones if necessary.
[autofit] Add blue-zone support for Devanagari.

This essentially moves the Devanagari script from the `Indic' hinter
to the `Latin' hinter.  Thanks to Girish Dalvi
<girish.dalvi@gmail.com> for guidance with blue zone characters!

* src/autofit/afblue.dat: Add blue zone data for Devanagari.

* src/autofit/afblue.c, src/autofit/afblue.h: Regenerated.

* src/autofit/afscript.h: Add Devanagari standard characters and
move data out of AF_CONFIG_OPTION_INDIC block.

* src/autofit/afranges.c: Move Devanagari data out of
AF_CONFIG_OPTION_INDIC block.
Move U+20B9, (new) Rupee sign, from Latin to Devanagari.

* src/autofit/afstyles.h: Update Devanagari data; in particular, use
AF_WRITING_SYSTEM_LATIN.
Formatting.