Some Linux distributions (notably Ubuntu) sets the --as-needed linker
flag by default, which makes the linker sensitive of the order of the
libraries the executable file depends on in the command line. Other
distributions (such as ArchLinux) do not set this flag by default. For
safety, this flag is explicitly turned off in both the Makefile and the
refimpl2-config script on Linux.

`cbinding/refimpl2-config` now puts `libmurefimpl2start.so` on the
"rpath" of the binary.

C programs can start Mu.

- Tested load_bundle, composite types and memory ops.
- Fixed a bug in insertelement.

In theory, all Mu client API functions are available to C, but not all
are tested.  Now a client in C is known to be able to create stack,
thread, handle traps and introspect stacks.

A C client can now call API functions to convert between primitive C
values and Mu handles.

C client can call MuCtx methods and close it now. It looks like it's on
the right track.

I am about to add some native-facing stuff, so make sure outdated JNR
libraries don't introduce bugs.

Existing code based on Int-based frame selectors should not break with
the help of RichMuCtx.

Consider the master branch of the microvm-spec as using the
goto-with-value form.

Useful for initialising reference fields to pre-allocated objects whose
references are held in global cells.

No C code written.