enable span-tag to accept finc-Solr-Schema (JSON/ldj) as input

[boferri]

(from my knowledge) currently, span-tag can consume Intermediate Schema (JSON/ldj). However, it might also be useful, if it can eat finc-Solr-Schema (JSON/ldj), because not all data source can be mapped to the Intermediate Schema.

[miku]

Yes, this is currently a limitation. I started to make the filters a bit more independent in the sift subpackage, which only requires certain small interfaces to be implemented to be able to use filters.

For example, a Go struct (which maps to JSON nicely) that implements SerialNumberer should be able to use an ISSN filter and so on.

What's left to do is to make SOLR schema implement these interfaces and then allow span-tag to map some name to some struct. I hope this will be done shortly.