+Add run-time ability to debug ePBL sensitivities

  Added the ability to passively run ePBL_column twice in a diagnostic mode and
then provide diagnostics of the differences in the diffusivities and boundary
layer depths that are generated with the two options.  This is controlled by the
new runtime parameter EPBL_OPTIONS_DIFF, which is an integer that specifies
which options to change or 0 (the default) to disable this capability.
Associated with this are the new diagnostics ePBL_opt_diff_Kd_ePBL,
ePBL_opt_maxdiff_Kd_ePBL and ePBL_opt_diff_h_ML, which only are registered when
the differencing is enabled.  For now, only changes associated with the settings
of EPBL_ORIGINAL_PE_CALC and EPBL_ANSWER_DATE can be evaluated, but this list
will grow as new options are added.

  As a part of these changes, there were some other reforms to the way that
MOM_energetic_PBL handles diagnostics, with the 2-d and 3-d arrays changed from
allocatable arrays with enduring memory commitments in the energetic_PBL_CS type
into simple arrays in energetic_PBL, relying on the fact that compilers will be
smart enough to avoid actually allocating this memory when it is unused to avoid
expanding the overall memory requirements of MOM6.  A number of allocate and
deallocate calls were eliminated by these changes.

  In addition, explicit 'units=' descriptors were added to numerous
register_diag_field calls to help identify inconsistent conversion factors.

  Also, the diagnostic of the number of boundary layer depth iterations was
added to the ePBL_column_diags, which enabled the intent of the CS and G
arguments to ePBL_column to be changed to intent(in).  The unnecessary extra
logic associated with the use of the OBL_converged variable in ePBL_column was
eliminated, but the results are uneffected.

  Because the MOM_parameter_doc files were changing anyway, and because this
commit is only a diagnostic change, about 6 spelling errors were corrected in
ePBL parameter descriptions as a part of this commit.

  All answers are bitwise identical, but there is a new runtime parameter and
there may be new diagnostics depending on the choice of a non-default value for
that new parameter.