Diplodoc search extension

This is an extension of the Diplodoc platform, which adds offline search functionality. It uses lunr search

The extension contains some parts:

Indexer {#indexer}

Extracts text information from documents. Prepares search index and search documents registry.

Instance methods:

add - Adds new entry to search index

release - Dumps index and registry for target language.

Implements client search worker interface. Uses prepared in indexer lunr index to resolve search requests.

Extends search score algorithm:

Adds tolerance behavior. tolerance=0 - only search for strict equal words tolerance=1 - also search for words with unspecified tail. word* tolerance=2 - also search for words with unspecified tail and head. *word*
Adds confidence behavior. phrased - default. Additionally scores results by found phrase length sparsed - Uses default lunr scoring algorithm.