Wire in config reloading on SIGHUP

This compiles, but probably crashes wildly. This handles config
reloading by attaching a handler for SIGHUP. This handler at this point
only allows modification (addition / removal / modification) of
datasources, but any value that is read through from configuration every
time will also support modification. Server thread count / listen
address / etc are not supported at this time (but they should not be
difficult to add).