Removed unused variable.

Now we've stripped out all the software-only, non-real-time rendering,
this variable is no longer needed.
Defining constants instead of using int literals.

As I've just been reading section 1.4 of The C Programming Language,
Second Edition, and wish to use good coding practices.  Indeed,
formulae like "semitone + (octave * SEMITONES_IN_OCTAVE_INT)" do
appear more readable.
Started work on using milliseconds, not seconds.

Extremely basic first steps of second attempt to do this.
Using int milliseconds, not float seconds.

Making good progress.
Refactoring tempo code.
Improved comment.
Ints, not floats.
Refactoring sliding code.

This'll make it slightly trickier to understand, but much quicker
to implement in C.
More refactoring of sliding.

Yes, technically this isn't to do with using milliseconds...
More refactoring.

This is arguably going too far, as we now have to perform the same
calculation twice.  Let's revert this.
Revert "More refactoring."

This reverts commit 4a2e5c00e2baeedf9ed5c24f2089f776486b9ff7.
Merge branch 'millis' into dev
Using int milliseconds, not float seconds.

Also refactored sliding slightly.

Squashed commit of the following:

commit 5443f7fad9bf7c37a2c4fd9200d520cd386551de
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Sat May 19 12:30:16 2012 +0100

    Revert "More refactoring."

    This reverts commit 4a2e5c00e2baeedf9ed5c24f2089f776486b9ff7.

commit 4a2e5c00e2baeedf9ed5c24f2089f776486b9ff7
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Sat May 19 12:29:54 2012 +0100

    More refactoring.

    This is arguably going too far, as we now have to perform the same
    calculation twice.  Let's revert this.

commit 532f82135c864f303b9a3b03f13aa0263a084251
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Sat May 19 12:26:51 2012 +0100

    More refactoring of sliding.

    Yes, technically this isn't to do with using milliseconds...

commit 1e6ec25bfa90f6e850d8ef9a90784c201618fd16
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Sat May 19 12:24:46 2012 +0100

    Refactoring sliding code.

    This'll make it slightly trickier to understand, but much quicker
    to implement in C.

commit 43f780d8cf6b985d6f90272e4477225e455f5150
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Sat May 19 12:20:12 2012 +0100

    Ints, not floats.

commit 20637ef56f894ec493cc87119c28e4dc7edd4887
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Sat May 19 12:13:22 2012 +0100

    Improved comment.

commit 2810411e8783d648e8c318e365dea1e74de03e70
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Sat May 19 12:08:53 2012 +0100

    Refactoring tempo code.

commit ad2cc5e77e0eff0c55308bd6f5aed567bbb43acc
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Sat May 19 12:00:41 2012 +0100

    Using int milliseconds, not float seconds.

    Making good progress.

commit 794e0a9f4d000924dfbac17969a24b9a9a316384
Author: Zoë Blade <zoe@bytenoise.co.uk>
Date:   Sat May 19 11:47:54 2012 +0100

    Started work on using milliseconds, not seconds.

    Extremely basic first steps of second attempt to do this.
Stripping out unused libraries.
Removed last imported library.

At least in Python, int() is essentially floor() for our purposes.
Merge branch 'master' into dev