Fix #4846 (Py_UNICODE_ISSPACE causes linker error) by moving the declaration into the extern "C" section.
Fix #4846 (Py_UNICODE_ISSPACE causes linker error) by moving the declaration
into the extern "C" section.

Add a few more comments and apply some minor edits to make the file contents
fit the original structure again.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator