Import spectral elements library

The subset imported here is sufficient for performing LGL interpolation
via cardinal functions.  This code does not yet implement Fornberg's
method, which would provide more efficient interpolation.
Import spectral element I/O code

This code provides a model for 2D LGL discontinuous spectral element
grids and a routine for reading them from a custom file format.  It also
implements interpolation under the assumption that the coordinate map is
restricted to translation and scaling.

Code quality is rather poor, but sufficient for the time being.
Add classes to model domain

These classes provide easy access to the bounding box of a domain and
its elements.
Add PixelMap class

Implements the translation and scaling rules for sampling an arbitrary
domain with a pixel grid.
Add ColorMap trait and implementations

Used to map Doubles to ARGB colors.
Import "diverging" colormap code

Provides conversion to and from the Msh color space and the generation
of "diverging" colormaps based on "Diverging Color Maps for Scientific
Visualization".
Add RenderSpec class

This class aggregates the details of a rendering operation.
Implement rendering actor

This actor renders the data from a single spectral element to a
BufferedImage according to a RenderSpec.  It prioritizes its messages
based on a sequence number and drops all messages with stale sequence
numbers.
Add DomainPlot and DomainRenderer classes

Note that this introduces a circular dependency.
Add application driver