Happy parse error messages should include more information

[harpocrates]

Right now, parse errors include only the line number. For example:

Calc.ly:40: Parse error

It would be helpful to include a bit more easily accessible info:

• the token on which parsing failed
• the column position of that token

[anka-213]

Would it also be possible to include information about what token was expected like in megaparsec? In theory that information should be available as well, but maybe it's not available in the generated code?