Improve schema type compliance, improve CONFIGURATION.md

[krassowski]

• Adds "item" to "array" types where missing
• Adds "null" type where default null is used
• Replace null with empty array ([]) where it made more sense (i.e. exclusion lists which are checked for truthiness rather than being None in the codebase)
• Improve script generating CONFIGURATION.md:
  • support arrays of types
  • fix double whitespace instead of single whitespace when combining strings
  • fix missing enumeration of accepted values

[ccordoba12]

Please rebase on top of the latest develop to get the fix to our tests in PR #231.

[ccordoba12]

Looks good to me, thanks @krassowski!