Add low-level interface for Bryan-Lewis mixing

The existing Bryan-Lewis initialization routine required users to store global CVMix parameters in a variable of type cvmix_global_params_type; now there is an interface that allows users to provide the Prandtl number and the max number of levels directly.

Add Schmittner tidal mixing

Merge pull request #72 from alperaltuntas/master

add Schmittner tidal mixing (sourcemods from njn01)

Fourth minor update to v0.80 (v0.84)

Bugfix -- with enhanced diffusivity turned off, KPP was inadvertently producing a non-zero diffusivity at the interface below the boundary layer in some instances. That bug has been fixed and a test has been added to the KPP stand-alone reg_test.

Third minor update to v0.80 (v0.83)

Qing Li added a routine to cvmix_kpp.F90 to compute the enhancement factor used for Langmuir mixing.

Second minor update to v0.80 (v0.82)

I did a quick check for trailing white space and was surprised to find a lot of it - this release cleaned that all up. I'm working on a github hook to prevent commits with trailing whitespace in another project, and plan on bringing that to CVMix as well once it is up and running.

First minor update to v0.80 (v0.81)

Bugfix for convection mixing (had an indexing error; rather than omitting the bottom layer we were inadvertently omitting the bottom two layers). Also added option to only apply convection mixing below the boundary layer.

KPP now supports LMD computation of turbulent scales

By default, CVMix continues to use the Danabasoglu, et al., formulation for computing turbulent velocity scales (where sigma is capped at some epsilon (0.1 by default) for both stable and unstable regimes... but an option now exists to use the Large, et al., formulation (where sigma is only capped for unstable conditions).

See paragraph preceding Eq (13) in LMD94 and paragraph preceding Eq (A3) in DLTGBM06 (doesn't quite roll of the tongue as easily as LMD94...) for more details.

Second minor update to v0.70 (v0.72)

Refactor cvmix_tidal to avoid computing time-invariant quantities in a routine that should be called every timestep.

First minor update to v0.70 (v0.71)

Remove unused argument to cvmix_coeffs_kpp_low (Stokes drift)

KPP now supports Langmuir mixing for surface waves

Development done at Brown University - updates KPP interface to allow Langmuir mixing.