Documentation, nodes, ast types and plugins

[ballercat]

This documents (and types) plugins, node parsers and ast.

[coveralls]

Pull Request Test Coverage Report for Build 147

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.05%) to 99.356%

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Totals
Change from base Build 133:	-0.05%
Covered Lines:	1883
Relevant Lines:	1883

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💛 - Coveralls