small fixes to the demand page memory

and a memory exception type
demand paged memory graduated

to plx.
DemandPagedMemory is now used in inflater.h

And therefore we come full circle to the adventure we started about 20
days ago.

The problem was that std::vector is not performant at all when it comes
to "deflate", because it has to come with lz77

for (int ix = 0; ix != count; ++ix)
output_.insert(output_.end(), output_[s++]);

that insertion causes lots of copies.

Along the way we have  had to invent
plx::Globals
plx::VEHHandler
plx::DemandPageMemory