num_waves and num_eqn for Euler_3d.
Make 3D Euler solver work with SharpClaw.
Merge pull request #66 from ketch/euler_3d_values

Euler 3d values
Correct Roe solver; add HLL solver for Euler eqns.
Roe averages in Euler solver are computed in a separate function.
Rebase branch onto updated master.