This Python function takes two optional kwargs: stack_size,
max_strings_per_rule. These each are unsigned int types and will be used
to update the YR_CONFIG_STACK_SIZE and YR_CONFIG_MAX_STRINGS_PER_RULE
configuration options in the matching engine, respectively. We found a
case preventing moving from cmdline yara to python-yara due to the lack
of control over these options in the Python module. This fixes that. I
suppose, at some point, it might be worthwhile to also implement a
get_config entrypoint as well.