Add (super basic) support for sending error messages out to the GUI
Increase HTML GUI message ring buffer size to 100
Add tentative support for named threads:

* Threads now accept an optional name argument
* If a thread already exists (and is running) with a given name, new
  threads with the same name aren't allowed to be created
Fix audible click heard when playing some samples:

Turns out to be an off-by-one-error with frame indexing! Fix is to
decrement number of frames by 1 :-)
Add basic non-enveloped sample playing synths:

Pros:
* Simpler design (uses less CPU)
* Supports modifying the rate whilst it's playing

Cons:
* Doesn't support envelopes
* Doesn't support playing parts of the sample
* Doesn't support negative rates (i.e. no backwards playing)