Fix NQP op documentation for nqp::exist*

It's existskey, not existkey
Merge pull request #124 from hoelzro/master

Fix NQP op documentation for nqp::exist*
[Configure.pl] turn prefix into an absolute path
add refs to more ops

moritz++
more ops
Saner git pull address

The http:// is more likely to work in limited environments, hence it will
work for more people trying to compile with --gen-X
Remove parasithic lookaheads

According to jnthn leftovers from when the LTM wasn't too smart