Make it easier to write unit test on a plugin

See test/weather_test.rb for an example
Add StubPlugin::load_plugin()

The class method returns the instance of the loaded plugin
instead of its class like StubPlugin::new_plugin()
Make conf in plugin configurable

Add []= and [] methods to ConfStub instances
Make options changable
Merge pull request #400 from zunda/better_plugin_test_pr

Make it easier to write unit test on a plugin
TDiary::IO::Base#style activates style automatically.
added prerequisites for bundler [fix GH-385]
Update source URL for weather information

NOAA changed URL from
http://weather.noaa.gov/weather/current/#{station_id}.html
to
http://www.aviationweather.gov/adds/metars/?station_ids=#{station_id}&std_trans=translated&chk_metars=on&hoursStr=most+recent+only
accordingly, URL is translalted each time the plugin treis to
fetch weather and updated permanently when the plugin is
configured.

The format of the table in the HTML page has also been updated.

Indents in test/weather_test.rb are fixed.
Merge pull request #403 from shugo/style_activation_fix

スタイルの自動有効化
update dependency
bump version to 4.0.2.20140201
use octorelease
Separate StubConfs between different tests

Stub for @conf was sharing the same class between
test/disp_referrer_test.rb test/weather_test.rb.
Typo is also fixed, from Stab to Stub.
added 2.1.0 and head into travis
Merge pull request #405 from zunda/weather_aviatoinweather_gov-pr

Update source URL for weather information
fix rvm name
Fix a typo

Stab ->
Stub
  ^
Merge pull request #406 from kou/fix-a-typo

Fix a typo
update dependency
use File.exist? instead of File.exists?