High level description of MAPL

Probably can be significantly improved.

README.md

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 # MAPL Repository
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+MAPL is a foundation layer of the GEOS architecture, whose original purpose is to supplement the Earth System Modeling Framework (ESMF).   MAPL fills in missing capabilities of ESMF, provides higher-level interfaces for common boiler-plate logic, and enforces various componentization conventions across ESMF gridded components within GEOS.
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+MAPL has 3 primary subdirectories:
+1. MAPL_Base - pretty much the core of MAPL as described above.
+2. GMAO_pFIO - this is a high level I/O layer that supports input and output as well as checkpointing for GEOS.   The layer heavily uses object oriented Fortran and is intended to be highly extensible.    The layer includes client-server capabilities that allow using a dedicated set of nodes to cache output before writing to disk, and is highly parallel.
+3. MAPL_cfio - this is a deprecated lower-level I/O layer that is generally replaced by GMAO_pFIO.    Not all of the strings have been cut yet.  Sometime soon, this directory will be eliminated.
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