Add 'C API' to the style guide (#1222)

Author: hugovk

documentation/style-guide.rst

@@ -74,6 +74,10 @@ presentation in the Python documentation.
 Other terms and words deserve special mention as well; these conventions should
 be used to ensure consistency throughout the documentation:
 
+C API
+  Python's `API <https://docs.python.org/3/c-api/>`_ used by C programmers
+  to write extension modules. All caps and unhyphenated.
+
 CPU
    For "central processing unit." Many style guides say this should be
    spelled out on the first use (and if you must use it, do so!). For

internals/parser.rst

@@ -711,7 +711,7 @@ When a pegen-generated parser detects that an exception is raised, it will
 is and it will unwind the stack and report the exception. This means that if a
 :ref:`rule action <peg-grammar-actions>` raises an exception all parsing will
 stop at that exact point. This is done to allow to correctly propagate any
-exception set by calling Python C-API functions. This also includes :exc:`SyntaxError`
+exception set by calling Python's C API functions. This also includes :exc:`SyntaxError`
 exceptions and this is the main mechanism the parser uses to report custom syntax
 error messages.