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/tests/scripts/depends-hashes.pl b/tests/scripts/depends-hashes.pl
index f57e7ed..92bcceb 100755
--- a/tests/scripts/depends-hashes.pl
+++ b/tests/scripts/depends-hashes.pl
@@ -58,11 +58,11 @@
     print "* Testing without hash: $hash\n";
     print "******************************************\n";
 
-    system( "scripts/config.pl unset $hash" )
+    system( "scripts/config.py unset $hash" )
         and abort "Failed to disable $hash\n";
 
     for my $opt (@ssl) {
-        system( "scripts/config.pl unset $opt" )
+        system( "scripts/config.py unset $opt" )
             and abort "Failed to disable $opt\n";
     }