Support Killing Processes From The Python Meterpreter

This PR adds support to the Python meterpreter for killing PIDs by adding the ```sys_process_kill``` function. This also fixes a small issue with the ```sys_process_close``` function where the type was incorrectly specified as ```TLV_TYPE_PROCESS_HANDLE```. The ```sys_process_close``` function also does not kill the process which more closely emulates the behavior of the native meterpreter implementations.

Testing:
- [x] Verify the post/test/meterpreter module finishes with 16 passed tests and 0 failures
- [x] Verify the kill command is now available from the meterpreter prompt
- [x] Verify the kill command kills processes