More flexible features

[zauguin]

Depends on #25. Be less restrictive when parsing feature specifiers.
Especially when loading Lua fonts or when using custom modes, the "features" might not be features in a OpenType sense. Then we might not want to limit the characters usable in the "feature" values more than necessary.
For lua-fonts this allows using the "features" as a general argument passing interface:

Example (assuming the existence of an appropriate apply_featurefile.lua):

\font "apply_featurefile.lua:file={somedir/somefile.fea};original={TeX Gyre Pagella}"

[u-fischer]

Looks very interesting. I will merge tomorrow, it is too late now. Do you have an idea for some new "mode" that could be used for tests (until something real comes up from the harfbuzz stuff)?

[zauguin]

@u-fischer The plain mode: (With some sample features)

plain_mode.tex:

fonts.readers.plain = function(spec)
  local f = font.read_tfm(spec.forcedname or spec.name, spec.size)
  local s = spec.features.raw.slant
  if s then
    f.slant = tonumber(s)
  end
  local b = spec.features.raw.bold
  if b then
    f.mode = 2
    f.width = tonumber(b)
  end
  return f
end

Example:

\documentclass{article}
\directlua{require'plain_mode'}
\font\cmrfont"cmr10:mode=plain;slant=1000;bold=500"
\begin{document}
abc\cmrfont def
\end{document}