add support for file repositories

fixes #37

see #33

Added an option (-s/--style) to allow to select
the style in every invocation of the bibliography
tag individually.

fixes #17

see #16

#19

In essence we withold application of the :latex filter until we
do html generation.

#14

#14

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.

the cited option will limit the bibilography to those entries
which have been previously cited on the same page using the
cite tag.

see #10

#1

#1