Get YamlMark instances for all events in Text.Libyaml

[afranchuk]

Having the source location of events within Text.Libyaml is useful for printing error/warning messages related to documents. If the marks are available, the Data.Yaml ParseException constructors could (possibly) include the mark related to the monad failure. I haven't looked in depth into the way the Aeson bindings have been done, so maybe that's not possible. But adding location information to errors in Data.Yaml.Parser should be possible. Having the marks in Text.Libyaml would be the minimum necessary to meet what I need (according to the libyaml documentation, start_mark and end_mark attributes are available for all events).

[snoyberg]

To start: I'd be open to a PR to Text.Libyaml to add new decoding functions which return the YamlMark together with the Event.

[afranchuk]

Yeah, I may have a PR in the not-too-distant (1-2 months) future. I don't immediately need the functionality, but I will.