add variable for c++ template: project, namespace, etc

[alanqian]

1. generic variable added: project, namespace
2. modified c/c++ guard for google style: PROJECT_FILE_H_
3. add variable for unit test(gtest): testclass, testvar

[muff1nman]

Thank you for the pr! A couple of thoughts:

1. We have a way to add user defined variables as implmeneted in Allow users to define custom variables to expand #58. I would rather keep the built in list of variables to a small common list. So try out Allow users to define custom variables to expand #58 and let us know if you run into any troubles.
2. Can you separate out the modifications to the c++ guard in a separate pr?
3. Indentation needs to be fixed.

Thanks!

[muff1nman]

Closing due to lack of activity