Invoke config.py instead of config.pl

git grep -Fl /config.pl | xargs sed -i -e 's!/config\.pl!/config.py!g'

Also:
* Change one comment in include/mbedtls/check_config.h.
* Change PERL to PYTHON in CMakeLists.txt.
diff --git a/scripts/apidoc_full.sh b/scripts/apidoc_full.sh
index bebab10..dfe1177 100755
--- a/scripts/apidoc_full.sh
+++ b/scripts/apidoc_full.sh
@@ -19,7 +19,7 @@
 CONFIG_BAK=${CONFIG_H}.bak
 cp -p $CONFIG_H $CONFIG_BAK
 
-scripts/config.pl realfull
+scripts/config.py realfull
 make apidoc
 
 mv $CONFIG_BAK $CONFIG_H