Adding support for composite glyphs: \[xxx yyy ...] and the

Adding support for composite glyphs: \[xxx yyy ...] and the
`composite' request.

* src/roff/troff/glyphuni.cc: New file for mapping groff glyph names
to Unicode-based glyph names.
* src/roff/troff/uniglyph.cc: New file for mapping Unicode-based
glyph names to groff glyph names.
* src/roff/troff/uniuni.cc: New file for canonically decomposing
Unicode-based glyph names.
* src/roff/troff/input.cc: Include unicode.h.
* src/roff/troff/unicode.cc, src/roff/troff/unicode.h: New files
for handling Unicode glyph names.
(composite_glyph_name): New function.
(token::next) <'['>: Handle Unicode glyph names and composite
glyphs.
(composite_dictionary): New dictionary for the `composite' request.
(composite_request): Implement `composite' request.
(init_input_requests): Add `composite'.
Alphabetically sorted.
* src/roff/troff/env.cc (tabs_save, tabs_restore): Removed (already
commented out).
(init_env_requests): Alphabetically sorted.
Removed `tas' and `tar' (already commented out).
* src/roff/troff/Makefile.sub: Updated.