Add dependencies on libedit, libgmp, and libffi.

Also simplify the way libs/pkgs are located and inserted into
makefiles and the .pc file.
Define PARAVM_EMULATE if libe_host is not found.
Add an initial .clang-format file.

The options in it so far are good, but clang-format still has
some issues with e.g. array formatting so be careful with it.
Use typeof for function pointer declarations.