Added Makefile target to install and uninstall

Added the "install" target in the main Makefile.
The new target does:
1. copy the lib/libhello.so file to /usr/local/lib
2. copy the include/hello.h and include/foo.h to /usr/local/include
3. run "ldconfig" to reload the dynamic library cache

Also added the "uninstall" target to clean up
Added integration test

Test if the installation (e.g. sudo make install) works