Create handler for SIGTERM to exit cleanly

[carsonharmon]

Sometimes when parsing a large file, or running a file through a complex parser, it might use up lots of resources and memories.

Create a signal handler to handle SIGTERM to stop tracing/execution and to dump results for processing.

[ESultanik]

This would likely require instrumenting libc.

We need to investigate to see if this is required to ensure that our current at exit handler gets run cleanly. If not, this is probably not necessary.