message: Updating miniapp comments
diff: // Twist Miniapp: Generate simple twisted meshes
  // ----------------------------------------------
  //
  -// This miniapp generates two types of Toroidal meshes; one with triangular
  -// cross sections and one with square cross sections. It works by defining a
  -// stack of individual elements and bending them so that the bottom and top of
  -// the stack can be joined to form a torus. The stack can also be twisted so
  -// that the vertices of the bottom and top can be joined with any integer
  -// offset.
  +// This miniapp generates simple periodic meshes to demonstrate MFEM's
  +// implementation of periodic domains. MFEM's strategy is to use a
  +// discontinuous vector field to define the mesh coordinates on a
  +// topologically periodic mesh. It works by defining a stack of
  +// individual elements and stitching together the top and bottom of
  +// the mesh. The stack can also be twisted so that the vertices of
  +// the bottom and top can be joined with any integer offset (for
  +// tetrahedral and wedge meshes only even offsets are supported).
  //
  -// Compile with: make toroid
  +// Compile with: make twist
  +//
  +// Sample runs: twist
  +// twist -ns 2
  +// twist -ns -2
  +// twist -ns 2 -e 4 -pm
  +// twist -ns 2 -e 6 -pm
  +// twist -ns 3 -e 8 -pm
  //
  -// Sample runs: toroid
  -// toroid -nphi 6
  -// toroid -ns 1
  -// toroid -ns 0 -t0 -30
  -// toroid -R 2 -r 1 -ns 3
  -// toroid -R 2 -r 1 -ns -3
  -// toroid -R 2 -r 1 -ns 3 -e 1
  -// toroid -R 2 -r 1 -ns 3 -e 1 -rs 1
  -// toroid -nphi 2 -ns 10 -e 1 -o 4
  -
  #include "mfem.hpp"
  #include <fstream>
  #include <iostream>
  