intermediate steo in improving doc system to doxygeb
avoid operators
Merge branch 'master' of git.dcc.fc.up.pt:yap-6.3

Conflicts:
	pl/modules.yap
more fixes
fix complaints about mixing term, term_t and yapterm.
get pred defs close to use as built-ins.
fix typo
fix small bugs from changing style_check
make sysgraph better
small fixes