Just-In-Time kernels

[camierjs]

Compagnon PR of MFEM's one.

• 2d: ./laghos -p 1 -pa -dim 2 -ms 10 -rs 1 -ok 4 -ot 3
• 3d: mpirun -n 6 ./laghos -p 1 -pa -dim 3 -ms 10 -rs 1 -ok 4 -ot 3
• 3d: mpirun --oversubscribe -n 12 ./laghos -p 1 -pa -ms 10 -rs 1 -ok 3 -ot 2

JIT: mass & force

JIT: mass, force & QFunction

| QP | N dofs   | FOM0   | FOM1   | T1   | FOM2   | T2   | FOM3   | T3   | FOM    | TT   |
| 512|     66342|   0.563|  20.833| 2.434|  10.473| 0.367|   1.684| 4.027|   8.984| 6.828|

Master

| QP | N dofs   | FOM0   | FOM1   | T1   | FOM2   | T2   | FOM3   | T3   | FOM    | TT   |
| 512|     66342|   0.536|  18.208| 2.785|  10.551| 0.364|   1.686| 4.024|   8.551| 7.173|