We added 2 macros A2_TEST_DIR and A2_TEST_OUT_DIR to pass tests in
`make distcheck`. A2_TEST_DIR refers to test directory. All output
files by unit tests are now created under A2_TEST_OUT_DIR directory.
Added .cc file for classes/structs that only provided by header
file. Defined non-POD classes' ctor, dtor in .cc file. Moved
implementation code in header file to .cc file for major
classes/strucsts.