Update gemspec: summary, description, and files. Also add json gem
dependency and update CHANGELOG and README with lots of new features!

Add a GROUP BY clause which yields correct SQL. (Incorrect query is
accepted by MySQL and SQLite but not PostgreSQL.)

Stop allowing full :conditions option to near_scope_options (was
deprecated, now it's gone). Update installation documentation.

Update to-do list and changelog.

Update changelog and bump version.

Update changelog, bump version, and change gem home page from
code.alexreisner.com to github.com.