Add poppler-0.18 support

This fixes build with newer poppler-0.18 and adds an ability to
choose hinting style (slight or full).
hinting improvements

Add hinting options to config file as well.
Add hinting documentation.
update-xpdf-poppler-rc is optional

update-xpdf-poppler-rc is Debian-specific config file generator,
shouldn't be general-enabled.
Adapt for poppler-0.20 API changes

first step, though...
one more step for 0.20 support

Fix mostly error handling. Drop an attempt to support both 0.18 and
0.20: too subtle changes are made.

Warning! This code is not working yet, but this step is required
for further changes, otherwise it will be one hellishly large
commit.
further depuplication

Deduplicate more methods.
Add deprecation warning method.
Make t1lib and freetype options deprecated: freetype is always used
now.
More cleanup