Have Bibliography::parse return Result instead of Option?

[ariroffe]

Hi, I'm the author of this crate, which uses biblatex: https://github.com/ariroffe/bib-unifier

I was testing it with some real files, which some colleagues gave me, and Bibliography::parse was returning None and failing to parse some of them. I managed to track down the issue to the following entry, which those files contained:

@inproceedings{conigliocorbalan,
  author    = {Marcelo Coniglio and Mar{\'{\i}}a I. Corbal{\'{a}}n},
  title     = {Sequent Calculi for the classical fragment of {B}ochvar and {H}alld{\'{e}}n's {N}onsense {L}ogics},
  booktitle = {Proceedings Seventh Workshop on Logical and Semantic Frameworks, with Applications, {LSFA} 2012, Rio de Janeiro, Brazil, September 29-30, 2012.},
  pages     = {125--136},
  year      = {2012},
}

The problem is merely that there is an extra \ before the i in Mar{\'{\i}}a. When that backlash is removed, the files parse correctly.

The thing is, parse was failing completely, without any explanation as to why, so all I can tell the end user is that there was a problem parsing that file. I'm new to Rust, and maybe this too much to ask, but would it not be more appropriate if parse returned a Result instead of an Option? (or at least to have another method that does return a Result). The Err variant could then detail which part of the original file was the cause of the parsing failure. I believe this could help users of the library such as myself.

[ariroffe]

See #16

[reknih]

The error reporting in biblatex is crap right now.

A rewrite of the whole parser is definitely on the slate and one priority for me is to provide good diagnostics that point to the actual syntax error (i.e. unexpected ' after backslash on line 1).

Until that happens however, your PR definitely provides a good quick fix that works with the current infrastructure.