elsevier_package: fixes reference harvesting for CONSYN

* adds a case for book references
* fixes exception handling
Merge pull request #6 from GiorgosPa/author-harvesting

elsevier_package: fixes reference harvesting for CONSYN
elsevier_package: fixes pep8 issues
Merge pull request #7 from GiorgosPa/author-harvesting

elsevier_package: fixes pep8 issues
elsevier_package: fixes on date and volume harvesting for CONSYN
Merge pull request #8 from GiorgosPa/date-volume

elsevier_package: fixes on date and volume harvesting for CONSYN