Be more tolerant of whitespace.

[laceysanderson]

Currently any whitespace at the beginning of a tag = value pair causes it to not be recognized as shown in @bradfordcondon example bibtext file: https://github.com/UofS-Pulse-Binfo/tripal_bibtex/blob/7.x-3.x/example/example.bib

We should be more tolerant especially since this makes the file Much more readable.

[bradfordcondon]

I was thinking about this: would it make sense to just split on _=_ and trim the 0 key to remove whitespace?

[laceysanderson]

I think we're better off making the regex more tolerant. We could end up with issues if there is an = in the value: tag = {lorem ipsum = latin nonsense}

[laceysanderson]

Also solved in @spficklin PR