examples: Add example code for user C modules, both C and C++.

Add working example code to provide a starting point for users with files
that they can just copy, and include the modules in the coverage test to
verify the complete user C module build functionality.  The cexample module
uses the code originally found in cmodules.rst, which has been updated to
reflect this and partially rewritten with more complete information.

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/unix/extra_coverage.py b/tests/unix/extra_coverage.py
index 1c028506e..b4808993a 100644
--- a/tests/unix/extra_coverage.py
+++ b/tests/unix/extra_coverage.py
@@ -49,6 +49,16 @@ print(buf.write(bytearray(16)))
 # function defined in C++ code
 print("cpp", extra_cpp_coverage())
 
+# test user C module
+import cexample
+
+print(cexample.add_ints(3, 2))
+
+# test user C module mixed with C++ code
+import cppexample
+
+print(cppexample.cppfunc(1, 2))
+
 # test basic import of frozen scripts
 import frzstr1