parse: Create messages from ParseErrors

parse: Rename ParseError messages to ParserError

tests: Tidy parse error test data

parse: Add function to fully format an error

tests: Always draw a task for ParseContext

parse: Add function to format a ParseContext for display

parse: Add function to format a ParseErrorException for display

tests: Document parse error data structures

tests: Fix draw_maybe ratio ...

I wrote this code while really tired and of course an off by one error
slipped in.

tests: Use a proper values for structural ParseContext tests

src: Check for None in all __eq__ methods ...

This lets us finally compare parse error exceptions and contexts of
different shapes.

i18n: Add new module containing a Message class ...

This Message class will be used to format localized text later.

tests: Move parser error tests to its own file

parse: Have parse run parse_file

parse: Add file parser

parse: Add directive parser

tests: Fix draw_wrong_statement_at drawing invalid values

tests: Note what we expect for test_parse_set_valid

tests: Copy tokens in template_test_invalid ...

This makes debugging easier as our input data isn't consumed.

parse: Add conditional statement parser

parse: Add Set node parse code ...

I've taken a different approach this time with my tests by avoiding
decorated functions where I can and adding big upfront documentation
about how things work.

I've deprecated the old decorated functions and hopefully will remove
them during a refactor and cleanup.

parse: Add statement parsing

tests: Document expected parse task

tests: Test parse_value error propagation

parse: Add code for parsing values

tests: parse: Clarify what error_on_token does

tests: parse: Use a mock class for note skipping

tests: Use a static parse context for tests

tests: Use a static token location for random tokens

tests: Use static tokens with static locattions