* Get rid of "structures" from RIGID_BODY and remove Find_Structure and related stuff.
* Update CMakeLists.txt build for public library.
* For classes where custom instantiations may be useful but cpp files exist, separate definition from cpp file.
* Remove unused stuff or stuff redundant with STL from TYPE_UTILITIES.
* Get rid of INTERRUPTS.* and its uses.
* Clean up ARRAYS_FORWARD.
* BLAS
* Do we still need DYNAMIC_LIST/STRUCTURE_LIST?
* Replace COUNT_BITS, integer_log with STL constructs.
* Remove Componentwise_Min_Max.
* Rename files whose contents are functions to match capitalization.
* Remove Inverse?
* Get rid of Robust_Arithmetic
* Remove argmax and argmin files.
* Remove exchange, Exchange, etc.  Use std::swap and move constructors instead.
* Remove MATRIX_POLICY.
* Clean up FILE_UTILITIES, use std::filesystem where possible.
* Clean out READ_WRITE.h and READ_WRITE_FORWARD
* Clean out STRING_UTILITIES
* Remove ARITHMETIC_POLICY.
* Remove Normalize.h
* Remove VECTOR_UTILITIES
* Resolve compilation with LEX/YACC.
* Remove ODE_SOLVER
* Clean up Geometry/Analytic_Tests facilities.
* Clean up Basic_Geometry classes.
* Can we remove these things now: SEGMENTED_CURVE_2D_SIGNED_DISTANCE, ...
* Remove BOX_*_INTERSECTION files, merge in with respective geometry.
* Move complex intersection stuff from SEGMENT_2D, TRIANGLE_3D, etc.  Separate out with SEGMENT_3D_TRIANGLE_3D_INTERSECTION and the like.
* Merge EXTRAPOLATION with EXTRAPOLATION_UNIFORM.
* For BLAH_UNIFORM with a BLAH base class, where nothing else derives from BLAH, merge and call BLAH.
* Remove LEVELSET_POLICY.
* Resolve LEVELSET_MAKER vs other ways of making level set.
* Clean out LEVELSET_UTILITIES
* Merge fast marching code into REINITIALIZATION as another function.
* Remove unneeded headers.
* Remove ARRAYS_UTILITIES
* Move LINEAR_INTERPOLATION_MAC_*D_HELPER, MULTILINEAR_INTERPOLATION to Incompressible.
* Remove PCG_SPARSE and PCG_SPARSE_SYSTEM
* Remove ACCUMULATE_HELPER.
* Remove SPARSE_MATRIX_PARTITION
* Remove PARTICLES_SUBSET
* Check for convergence on all tests in testing suite.
* Create unit tests for everything 
* Fix Determinant for singular larger matrices.
* Decide what to do for IO for diagonal and symmetric matrix.
* update the qt viewer to work on wayland
  - what: starting with ubuntu 21.04, the display server is Wayland
  - problem: the qt_viewer is not working on wayland
  - workarounds: 
    - log into "ubuntu with Xorg" (use the older X11 display server)
    - set QT_QPA_PLATFORM=xcb (uses the XWayland compatibility layer to allow legacy X11 applictions to run on top of Wayland)    
