Take into account source directory from original configuration for the generated repository links (#152)

* Allow the test environment to keep the originally sat 'source' value.

* Add a test case and a fix for the ignored source setting in the configuration file.

* Prepend the TEST_DIR only when the source configuration is not set to an absolute path (making it absolute in the process)

* Fix the definition of the relative repository paths, and fix the test feature to properly use the configured source directory.

This permits custom attributes to be passed to the bibliography list
such as `reversed` or `start` to permit custom numbering.

See inukshuk#148

See #147

See #147

{} could be matched arbitrarily inside of a {} pattern, in addition to
the expected behaviour of nested pairs. (oops)

Closes #143

See #139

test-unit dependency for cucumber should be specified as >= 2.2

Also add Ruby 2.3.0 to the Travis CI configuration.

Make bibtex converter use configured filters.

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

Add filter for \superscript LaTeX command

This filter converts \textsuperscript latex formatting into <sup> html
tags. It should be used before the `latex` filter to prevent premature
stripping of {} groups.

Also adds superscript to the default filters and documents the
bibtex_filters parameter in README.md

References inukshuk/jekyll-scholar#132

Details page page.title variable should use LaTeX filtered entry

See #129

See #129

Export authors into an array under entry.author_array

This permits easier iteration over an arbitrary number of authors.