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/3rdparty/everest/CMakeLists.txt b/3rdparty/everest/CMakeLists.txt
index 18c8731..782c0c5 100644
--- a/3rdparty/everest/CMakeLists.txt
+++ b/3rdparty/everest/CMakeLists.txt
@@ -10,7 +10,7 @@
 
 list(APPEND everest_inc ${CMAKE_CURRENT_SOURCE_DIR}/include ${CMAKE_CURRENT_SOURCE_DIR}/include/everest ${CMAKE_CURRENT_SOURCE_DIR}/include/everest/kremlib)
 
-execute_process(COMMAND ${PERL_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/../../scripts/config.pl -f ${CMAKE_CURRENT_SOURCE_DIR}/../../include/mbedtls/config.h get MBEDTLS_ECDH_VARIANT_EVEREST_ENABLED RESULT_VARIABLE result)
+execute_process(COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/../../scripts/config.py -f ${CMAKE_CURRENT_SOURCE_DIR}/../../include/mbedtls/config.h get MBEDTLS_ECDH_VARIANT_EVEREST_ENABLED RESULT_VARIABLE result)
 
 if(${result} EQUAL 0)