Refinements in Russian stemmer.

Updated search query cleaning algorithm to be closer to indexing clea…

…ning algorithm.

Added fallback for MySQL 5.6, running tests on old PostgreSQL versions.

Fixed highlighting of found words with hyphen.

Updated dependencies.

Fixed failing recommendation SQL for word_count=0 when only a title i…

…s present (SQLSTATE[22003]: Numeric value out of range: 1690 DOUBLE value is out of range in 'pow(`db`.`m`.`word_count`,-0.5)').

Fixed lost strtolower call for keywords. Adjusting relevance.

Updated README.md and comments.

Updated README.md

Some improvements in Russian stemmer.