Replace parser with something more lenient

[akx]

We'd want a parser that's more lenient and would process things that don't smell like valid syntax as just literals.

This would fix e.g. #750, #777, #755, etc.

Maybe... https://matklad.github.io/2020/04/13/simple-but-powerful-pratt-parsing.html

[odie5533]

As a shorter-term solution, slightly better error reporting would be very helpful:

• Which file had the syntax error
• Noting clearly that pyparsing errors are user syntax errors that the user can fix (rather than an internal issue)

TBH the yaml syntax I saw seemed fine? Just in my case I had no idea what the underlying issue was