Introduce a purely internal server clock with control-rate resolution.

** Highly experimental and subject to change/removal **

Clock uses a two-channel bus to measure ticks at control-rate. First 
channel is of range 0 -> 2^24 (the max resolution of the server) and 
on rollover, the second channel is incremented.

Potentially useful for measuring/managing time within synths. 
Let's see...

Introduces new functions:

* server-clock-n-ticks
* server-clock-uptime
* server-clock-time
* server-clock-drift

A new group (at the beginning of them all):

* foundation-timing-group

And a two-channel global clock bus:

* server-clock-b
Rename server-clock-tick-b to server-clock-b
improve docstrings for server sync functions
Re-order clock bus channels - now [small-tick big-tick]
Add some synths for playing partial parts of buffers.
Improve ugen docstrings
clean up ugen metadata
start adding metadata for loopbuf extra ugen - not complete (is silent!)
Replace default buffer players with a new design capable of playing parts
of a synth specified by start and and values (between 0 and 1).

(def f (freesound 1234))

(f :start 0.5 :end 0.6)