tests: Document parse error exception codes

src: Rename syntax to token

parse: Remove SyntaxType ...

Once again I find myself in the pattern of having a useless 'type' value
that just complicates my life. In this case the correct appproach is to
output the AST directly.

parse: Parse text and bools to AST types

tests: Clarify function documentation

tests: Refactor mid-test assumes in to custom draws ...

This should help with performance as Hypothesis as we no longer need to
do complex unrelated draws first.

parse: Handle parent_context in template_parse_invalid

tests: Split up parser tests for empty cases

tests: Add template_parse_invalid

tests: Add a template for parsing valid syntax

parse: Have parse_bool handle contexts properly

parse: Allow attaching a ParseContext to a ParseErrorException

tests: parse: Clean up some includes

tests: parse: Move bool tests to its own file