Implement new AMReX tagging format

[maximumcats]

PR summary

The refinement scheme from AMReX-Codes/amrex#1166 is implemented. Rather than using the Fortran tagging namelist, applications may use the inputs file. The scheme looks like:

amr.refinement_indicators = dens temp

amr.refine.dens.max_level = 1
amr.refine.dens.value_greater = 2.0
amr.refine.dens.field_name = Density

amr.refine.temp.max_level = 2
amr.refine.temp.value_less = 1.0
amr.refine.temp.field_name = Temp

amr.refinement_indicators is a list of user-defined names for refinement schemes. For each defined name, amr.refine.<name> accepts predefined fields describing when to tag. In the current implementation, these are max_level (maximum level to refine to), start_time (when to start tagging), end_time (when to stop tagging), value_greater (value above which we refine), and value_less (value below which to refine), and field_name (name of the string defining the field in the code). If a refinement indicator is added, either value_greater or value_less must be provided. (In the future we will support other refinement schemes such as gradients.)

A wdmerger setup is converted to the new scheme as a test.

PR checklist

• test suite needs to be run on this PR
• this PR will change answers in the test suite to more than roundoff level
• all newly-added functions have docstrings as per the coding conventions
• the CHANGES file has been updated, if appropriate
• if appropriate, this change is described in the docs

[zingale]

tests: http://groot.astro.sunysb.edu/Castro/test-suite/gfortran/2020-09-29-001/index.html