default to twitter api version 1.1
implement tweet search
twitter.rb: fix the usage of twitter 1.1 api, see:

we need to put the 1.1 prefix out of default site,
otherwise Twitter#authorize_url! and Twitter#authorize!
would break. this way, we could also make the user
who wants to use 1.0 api work more easily, and avoid
breaking the compatibility who calls Twitter#get or
Twitter#post directly.
twitter.rb: let's make query always means query string.
twitter/test_api.rb: restore the tests