Convert int, float, and bools from ENV['DATABASE_URL'] query args

Previous title: SQLite3 busy_timeout function requires an int argument

This resolves an exception seen when calling `rake db:create` with a DATABASE_URL and a timeout argument:

```shell
DATABASE_URL="sqlite3://localhost/db/test.sqlite3?timeout=500&pool=5" bundle exec rake db:create
can't convert String into Integer
gems/activerecord-3.2.9/lib/active_record/connection_adapters/sqlite3_adapter.rb:31:in `busy_timeout'
...
Couldn't create database for {"adapter"=>"sqlite3", "timeout"=>"500", "database"=>"db/test.sqlite3", "host"=>"localhost", "pool"=>"5"}
```