Add suggestions for auto-complete during indexing

[anupdhml]

To improve auto-complete queries, we can add suggestions when indexing documents.

https://www.elastic.co/guide/en/elasticsearch/reference/current/search-suggesters-completion.html#indexing

Start by tokenizing author/title fields and adding them as suggestions. Eg: we should get a match on "Bhairab Aryal" when querying for just "Aryal" (under current implementation, queries have to start with "Bhairab").

This can be later extended to support things like synonyms as a suggestion.

[aishraj]

Its mostly a nice to have, but we can do it using Python or something. Anup can work on this.

[aishraj]

This would enable us to search by last name etc.