Improve error reporting

[lmichaelis]

At the moment, phoenix only reports some failures using custom exception classes. Ideally, any failure which needs to be reported to the user should be wrapped in a custom exception class.

There is also a discussion to be had about using exceptions at all. It might be better to report failures using std::optional or a custom std::expected structure than throwing exceptions since some codebases don't allow exceptions at all.

Since this is a parser library, failure can occur more often than usual thus performance is also a point to keep in mind when using exceptions to report parsing failures.