Feature/bmauer/markup docs in source

[bena-nasa]

@JulesKouatchou @tclune
This PR brings the markdown files I added to develop. It should be obvious from looking at the details of the files changed in the PR what was added. Note that one of the markdown files (the one for PFIO) referenced some pictures to illustrated how the server worked. I had to add the PNG files to the directory with the markdown file so it would still display the pictures.

It looks like I added a .md file for
ExtData2g
History
PFIO
Arithmetic Parser
Error Handling Macros
Regridding Methods
ExtDataDriver.x
Regrid_Util.x
CapGridComp

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Trivial change (affects only documentation or cleanup)

Checklist:

• I have tested this change with a run of GEOSgcm (if non-trivial)
• I have added one of the required labels (0 diff, 0 diff trivial, 0 diff structural, non 0-diff)
• I have updated the CHANGELOG.md accordingly following the style of Keep a Changelog

[bena-nasa]

@JulesKouatchou I added a wiki page about MAPL CapGridComp and added a markdown file with the same contents to this branch