DATASOLR-134 - update documentation on per field facets

Per field facets can by adding FieldWithFacetParameters to FacetOptions.
Though this feature was not documented within reference manual. Added an
example to the facet section.
DATASOLR-104 - Enable multicore support via configuration

Via the multicoreSupport attribute within EnableSolrRepositories it is
now possible to bootstrap multiple repositores with different templates
dynamically created for the registered  types. 

Please note that multicore support will only work if the domain types
are properly annotated with SolrDocument providing required
core/collection information.