* Makefile.am: Add unit-tests
* cfg.mk: Make syntax-check work with unit-tests/
* configure.ac: Add unit-tests/Makefile
* tests/Makefile.am: Remove unit tests
* unit-tests/Makefile.am: New file with unit test rules
* unit-tests/*.c: Moved from tests/
* unit-tests/files: Moved from tests/

unit-tests/ is for library/API unit testing.
tests/ is for testing wget2 utility.