Added grams to the index

Allows to match before we get complete subword. Also, does not hide
previous matches while we typed past the sub-word boundary. Still does
not work if starting from the middle of word.
Improve splitting on known acronyms/abbreviations in use

Before, searching for directory would not pick RAMDirectory because
WordDelimiterFilterFactory did not see this as case change. So, we have
some manual assistance.