Don’t print rest message if silent TL is true
Don’t shortcut out when note is a rest within trigger_synth

* short-circuit on rest should have already happened in a higher fn
  such as play. This just adds extra overhead on *every* note trigger.
use util#log for printing debug messages from server
disable debug mode by default and rename log file to debug.log
Minor server optimisations:

* Cache debug_mode value locally to avoid having to call repeatedly
* Don’t create debug message strings and call log function if in debug_mode
* Move position_codes into a local in-emory map rather than a fn with a
  literal map
* Send ints in OSC message where server spec requires them (was occasionally
  incorrectly sending floats which the server must have handled gracefully)
* Don’t call sched_ahead_time fn for synth triggers as delta doesn’t need
  to be calculated.
* Avoid calling .to_i multiple times on the same node