By default - and prior to this - the top level library i work.
It is possible to specify top level library, via prefix in Manifest top_module value as described in updated documentation.

In summary:
- top_module = topmodule -> Default, top_library = work
- top_module = .topmodule -> top_library from Manifest library
- top_module = ?.topmodule -> top_library autodetected, experimental, used in test 114

testsuite Makefile.ref files have been updated with TOP_LIBRARY. Where TOP_LIBRARY was hardcoded (most often work), it have been replaced by TOP_LIBRARY.

Test 008 command change: changed to ghdl ... work.module (prior work. was not included) Compile output is identical for both commands.
(included in this commit)

Test 114: Manifest.py needs to be updated: syn_top value must start with ?. to autodetect top library (included in next commit)