Allow jruby failures on Travis CI for now.

There's some issue with the SQL generated by the JDBC adapter.
Work around protected sanitize_sql_array in Rails 4 for now.
Add Ruby 2.0.0 and allow failures on Travis CI
use i18n < 0.6.2 or > 0.6.2

Due to https://github.com/svenfuchs/i18n/issues/192
i18n 0.6.2 breaks ruby 1.8 compat
alter .pg_search_multisearchable_options

nest :against and friends under model name that
they should apply to e.g.
'PgSearch::Document' => {:against => :col}
verify multisearchable w/ multiple document models

duplicate and update tests against
PgSearch::Document to confirm identical behavior
w/ different model
intro PgSearch.multisearch('MySearchDocument', query)

PgSearch.multisearch(query) still delegates to
PgSearch::Document.
verify Multisearch::Rebuilder w/ multiple document models

Update and duplicate tests to confirm same behavior
whether PgSearch::Document or CustomDocument.
Heavily refactored to use shared examples.
update PgSearch::Multisearch.rebuild

Add logic to utilize new document_model arg.
add multisearch_model generator

Generate custom document models identical to
PgSearch::Document.
use connection from MultisearchableModel

PgSearch::Document may not be present.
add examples for custom document model usage