Use package_data instead of data_files

The previous method using data_files would always install these files in
the system directory, even when doing a user install (setup.py install
--user). get_python_lib() always returns the global python path, so the
manual path calculation would be wrong in this case. Instead make use of
package_data which will install the files in the correct location.

Fixes #22

CCCS and CCVS are not TwoPortElement, but TwoPinElement.

fix typos and English