Clean up MegaLinter errors and warnings

[wesley-dean-gsa]

MegaLinter found a bunch of things that need to be tidied up, some of which can be done automatically and some of which (e.g., security ones) may involve a little more manual intervention.

[wesley-dean-gsa]

The PR (#134) is more current with regards to updates on the progress for this.

tl;dr: we're mostly done with most of the fixes. There are just a few left to tidy up and we can close this out.

[wesley-dean-gsa]

The v8r linter error involved a missing field in the tool's validation schema; this was documented in tcort/markdown-link-check#355 and resolved in SchemaStore/schemastore#3972. If MegaLinter runs again, the JSON_V8R checks that were failing for .markdown-link-check.json will now pass.