Fix numerous minor issues in WG and VBF modules resulting from running first full integration tests.
Add solution evaluation functions to WGBasis.
Mesh: add fe_coords to exported interface, and new function nb_side_with_mesh_coords
Poly: add zero_poly_vec and value_at method for polyvectors.
Fix failure to account for boundary sides in WGBasis.solution_wgrad_on_interior.
Convert boundary projections to use coefficient arrays instead of polynomials.
Add boundary side count function to Mesh.
Remove cache parameter from VBF interface functions, just precompute the projections in the VBF_a_s constructor instead.
New Sol module with solution evaluation related functions.
WG: Reworked rhs vbf related functions to not use a mutating cache for boundary projections.
VBF: Implement sparse matrix function, not currently used because sparse solver has not yet been found.
Move tests back to top later.  Add proper test of WG method.  2d case working, 4d needs sparse matrix solver to be implemented.
Specialize constant projection for efficiency.
Mesh: New function num_non_boundary_sides_for_fe.
Sol: Rename various items and and implement grad error.
Rename bel_num to beln.