Handle building/packaging using `paver`...

Handle building and packaging using [`paver`][1].  This commit removes
`setup.py` from the repository, and adds `pavement.py`.

Building source distributable
=============================

The file, `pavement.py`, contains the instructions necessary to build a
source distributable of the `dmf_control_board` package containing:

 - Firmware Arduino sketch.
 - Compiled firmware `.hex` files, which can be flashed using, e.g.,
   `avrdude`.
 - Python API for interfacing with the hardware device.

To build a source distributable using [`Paver`][1], run the following
command from the root of the repository:

    paver sdist

Notes
=====

 - [`Paver`][1] must be installed before running `paver sdist`.  This
  can be done by running:

     pip install Paver

  However, as of [`aa5a1684`][2], the `paver-minilib` functionality is
  [broken][3].  The `paver-minilib` is used to package a minimal `Paver`
  implementation within a created source distributable, to allow the
  source package to be installed on a system using:

     python setup.py install

  As a temporary workaround, a patched version of `Paver` can be
  installed using:

    pip install -e git+https://github.com/wheeler-microfluidics/paver@master#egg=Paver-dev

 - Flags to be used when building firmware may be specified using the
   `--sconsflags` command-line argument.  For example:

     paver sdist --sconsflags="SKETCHBOOK_HOME=$HOME/sketchbook ARDUINO_PORT=/dev/ttyUSB0"

 - [`Paver`][1] does _not_ need to be installed on a system to install
  from a packaged source distributable.

[1]: http://paver.github.io/paver
[2]: https://github.com/paver/paver/commit/aa5a16843433607d6949a7e13dfb783a329e9620
[3]: https://github.com/paver/paver/issues/122