Move maybeSymbolParser, and possibly also allSymbolParser, to another repo

[jvoigtlaender]

I guess one could argue that this maybeSymbolParser does not really belong into this repo, since it is neither used anywhere in the repo itself, nor is in any way logic-specific.

Originally posted by @jvoigtlaender in 34d3aea

[jvoigtlaender]

Also applies to

logic-tasks/src/Formula/Parsing.hs

Lines 107 to 108 in 34d3aea

	instance Parse a => Parse (Maybe a) where
	parser = (tokenSymbol "Nothing" >> pure Nothing) <|> (Just <$> lexeme parser)