Fixes Neumann bc and TPF for MPFA-O

[bishtgautam]

• TPF now correctly accounts for dot(n_face,dist_vector).
• For TPF, the contribution from boundary faces is not included for flux across an internal faces
• The computation of the transmissibility matrix is updated for Neumann BC.

[codecov-io]

Codecov Report

Merging #101 into master will increase coverage by 3.39%. The diff coverage is 58.82%.

@@            Coverage Diff             @@
##           master     #101      +/-   ##
==========================================
+ Coverage   81.90%   85.29%   +3.39%     
==========================================
  Files          45       46       +1     
  Lines        9973    11823    +1850     
==========================================
+ Hits         8168    10085    +1917     
+ Misses       1805     1738      -67     

Impacted Files	Coverage Δ
src/tdyutils.c	85.32% <0.00%> (-2.38%)	:arrow_down:
src/mesh/tdycoremesh.c	94.91% <100.00%> (+2.06%)	:arrow_up:
src/mpfao/3D/tdympfao3D_core.c	98.42% <100.00%> (+0.88%)	:arrow_up:
src/mpfao/3D/tdympfao3D_ts.c	98.26% <100.00%> (+0.63%)	:arrow_up:
src/mpfao/3D/tdympfao3D_steady.c	100.00% <0.00%> (ø)
src/mpfao/3D/tdympfao3D_ts_dae.c	0.00% <0.00%> (ø)
src/mpfao/3D/tdympfao3D_ts_transientvar.c	0.00% <0.00%> (ø)
src/tdyrichards.c	100.00% <0.00%> (ø)
src/tdytpf.c	98.97% <0.00%> (+0.19%)	:arrow_up:
src/mpfao/3D/tdympfao3D_snes.c	97.67% <0.00%> (+0.37%)	:arrow_up:
... and 18 more

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[ghammond86]

Are you okay with me merging even though the patch has lower codecov coverage?

[bishtgautam]

Yes, I'm okay with lower code coverage.