Improves SQLite FTS based search and sets it as default.

1. Uses sensible heuristics for exact match ranking
2. Allows boolean operators for more control [AND, OR, NOT]: hello NOT world matches "hello" but not "hello world"
3. Allows explicit prefixing search: hell* worl* matches "hello world"
4. Allows exact searches: "hello world" matches only "hello world"
5. Defaults to final word prefixed search: hello wor matches "hello world"

Also, removes porter stemming, and recognizes -_ as tokens.