add reset_context to lib

hapic/__init__.py

 output_file = _hapic_default.output_file
 generate_doc = _hapic_default.generate_doc
 set_context = _hapic_default.set_context
+reset_context = _hapic_default.reset_context
 add_documentation_view = _hapic_default.add_documentation_view
 handle_exception = _hapic_default.handle_exception