Implemented tape sync output.

The only issue with this is that time is now measured in the dizzyingly
fast realm of microseconds instead of the comfortable world of
milliseconds.  This is probably overkill, and will lead to the
sequencer having a possible issue every 70 minutes (see
http://arduino.cc/en/Reference/Micros for details) instead of every
50 days (see http://arduino.cc/en/Reference/Millis for details).

Squashed commit of the following:

commit fb833068b0ead6a05f217c10dac9d9893437be73
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 22:49:50 2012 +0100

    Bugfix in testing code.

commit 128dd657eb9312090c5dd3486e655abbbc4abaf9
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 22:38:56 2012 +0100

    Stepper now uses microseconds, not milliseconds.

    The Stepper 1 prototype interface still seems OK, but the tape sync
    still isn't working...

commit 27359db89cf7b5cbea059d3368773c6438861aba
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 22:19:20 2012 +0100

    Looks like no tape sync today.  Shame.

commit 43b9671a892e76e6e6aa62a3a3b12661e18b8b41
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 22:11:34 2012 +0100

    More thorough / realistic test.

    Added delayed start and stop, so there's a buffer of paused sequencer
    either end of the .wav file.

commit 1563334705b70a5d9c237ea171056fdc5cfeb5ba
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 22:05:48 2012 +0100

    Doctor, we have a pulse!

    ...only compared to the MC-4 reference pulse I'm working to at http://stevewoodward.posterous.com/roland-mc-4-sync-tones , the pitches sound too low frequency, and the clock sounds too high frequency.

    Amendment: listening to the references again, the clock sounds OK
    to me, leaving just the carriers to fix.

commit 4b61ea71aa677f0209497fae6393d2fa5575919b
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 21:49:44 2012 +0100

    Getting there...

    It's not working yet, but now it's at least making a noise, albeit
    a constant one.

commit caa7a4292055d639cb10fe06fba3cf676d456445
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 21:47:40 2012 +0100

    Tape sync combines trigger and gate into one single signal.

commit d8336304fe669c0567a5d45b6e9d3eb281b6358b
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 21:46:58 2012 +0100

    Timing fix.

    It would also help if we actually told it to play.

commit c0e9c3dcbaac97a3e36fac4c3e4aae6e775775c5
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 21:37:54 2012 +0100

    That's one bug fixed in the test code...

commit e41c7bf51d601140731e74d385ba2e601b996fd6
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 21:33:53 2012 +0100

    Incrementing time would help...

commit 35e7af591c78ed9a26cb283cfe35a505bde656bb
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Fri May 25 21:31:16 2012 +0100

    Set up means of testing tape sync output.

    It doesn't work after all.

    I'm using the output code from commit
    315b2708a6961039e20b6f937ce53454308d2ac0, modified everso slightly.

commit acdd72946c2b8c03f479aeb44cf8a5146e52dcc2
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Thu May 24 14:14:52 2012 +0100

    Added tape sync trigger output.

    Completely untested, aside from making sure the syntax is valid.
    (I'm not sure how to test it without doing some soldering and buying
    an oscilloscope, or making a wave file writer, etc.)

commit 9536f8f3f17abe548f1544d0922221f6ce95724c
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Thu May 24 13:57:42 2012 +0100

    Renamed Sync to DIN Sync.

    This is to avoid confusion with tape sync.
Removed tape sync output.

I'll sleep better at night if Stepper is more stable and simple,
rather than boasting features it might struggle to properly provide.

Revert "Implemented tape sync output."

This reverts commit 225b6c12d0ae168229b4ad35574ad1a78dd5cc22.