All documentation is built in obj/doc (resp. doc/ if you do a stand-alone build).
Use `make docs' to make the whole documentation or `make userdocs' resp.
`make progdocs' for user manual resp. developer's guide.
over EFence and also hopefully smaller memory overhead, but sadly it's non-free
for commercial use).
If the DMALLOC_OPTIONS environment variable is not set, switch on `reasonable'
checks by default.
Also introduced mb_allocz() for cleared mb_alloc().
