Simplify how standard elements are constructed.

We now avoid the use of the 'equi-spaced' quadrature rule.
Merge branch 'release/v0.2.0' into develop.
Rework how quadrature rules are stored/tabulated.
Refactor the Elements classes.
Remove some antiquated docstrings from BaseBasis.
Inline the xbasis_at class of methods from BaseBasis.
Apply @chop to m132 and m460 in BaseBasis.
Eliminate an unnecessary local variable from BaseElements.
Allow .get() and .set() to work on unallocated Matrices.
Switch to lazy evaluation of constant matrices.
Remove leading _ from public BaseBasis members.
Simplify how compound operator matrices are obtained.
Move to an improved lazyprop implementation.
Make matrix row slices more flexbile.

It is now possible to slice uncommitted matrices.
Implement volume anti-aliasing of the flux and its divergence.

This can be enabled via the "anti-alias" key in the [solvers]
block of the configuration file.  Permitted values are:

  none [default] | flux | div-flux | flux, div-flux

When set to anything other than none it is necessary to specify
the quadrature rule name/degree in the relevant elements sections
which is done via:

  quad-pts = rule | rule-name
  quad-deg = int
Merge branch 'feature/quadrature' into develop.
Update and cleanup quadrature rules.
Refactor the bases.
Rename 'bases' to 'shapes'.
Eliminate an unnecessary MPI barrier.