csi_string_new() duplicated the bytes which was not what was desired, so
implement a csi_string_new_for_bytes() to take ownership and prevent the
leak that was occuring, for example, every time we create a new font face.
Add a CairoScript interpreter library and use it to replay the test output
for the CairoScript backend. The library is also used by the currently
standalone Sphinx debugger [git://anongit.freedesktop.org/~ickle/sphinx].
The syntax/operator semantics are not yet finalized, but are expected to
mature before the next stable release.
