Better error reporting #9
Description
Errors are difficult to read and interpret by users, especially when parsing the expression grammar fails. There are several crates to format diagnostic messages on source code snippets in the terminal, including chic, annotate-snippets, codespan-reporting, and codemap-diagnostic, which could be used to format expression parsing errors in a more user friendly way.
It would also be useful to return more detailed error messages from rules in the grammar, especially when parsing dates/times that don't conform to the specified format fails. It is, however, not clear whether this is possible with rust-peg because conditional actions return Result<T, &str>.