The bibtex converter class was not making use of the `bibtex_filters`
global configuration option.

This permits easier iteration over an arbitrary number of authors.

Change test-case to use the global configuration value instead of the tag option for deciding to output the raw bibtex entry.

See #117

fixes #112

this time add add tests to prove it

fix #57

add support for file repositories

see #27 and #28

#19

Normalize tag parameters using Ruby's OptionParser. This
breaks the API but gives us a standard way of handling
parameters going forward.

This commit also adds optional prefixes used by the
bibliography, cite and reference tags. See #12.

#1

#1