set PKG_CONFIG_PATH to the local opam prefix (to find libminios)
and also remove detection of OCaml 4.00.1 from the config script
Remove support for the 4.00.1 runtime, and only support 4.01.0

There are a growing number of 4.01.0-only libraries, and packaging
on most distributions has improved now such that it's reasonable
to require 4.01.0 only.  We also need to prepare for 4.02.0 soon,
and there's no way we can support three concurrent versions of the
compiler.
Support compiling on ARM