Updated EHFLD to use lookup table. Accuracy of TRC and TRS using lookup
table has been tested outside this code. Results and code can be seen on
Torngat in directory
/home/pbellive/src/test-filtering/ehfld-test-filtering/interpolate-on-mesh/

Results are identical, except for relative error of ~1e-4 at two
transmitters for quadrature component at 5500Hz. Test results on bigger
mesh pending.