Corrected bibliography template

Avoids error:
```
Liquid Exception: Variable '{{ entry.abstract %}' was not properly
terminated with regexp: /\}\}/
```

see #69

see #65

Added the 'numbering' option in the configuration for unordered publicat...

Instead of the 'numbering' option, 'bibliography_list_tag' and 'bibliography_item_tag' have been introduced. Defaults.rb has been updated.

see #59

fix #57

fix #57

Details link available on bibliographic references template

see #44

see discussion at #44 for details

Added test: Multiple Citations in a list using liquid variables