Add more info about the minimum_should_match syntax. Also rename
"minimum_match" and "minimum_number_should_match" references to
"minimum_should_match"

From:
http://lucene.apache.org/solr/4_3_1/solr-core/org/apache/solr/util/doc-files/min-should-match.html
Edited links to min-should-match

Closes #454