@kou's implmentation
Edited defnition of StubPlugin::inherited.

Supplying a block to module_eval(0 seems to be more readable.
Created a class method StubPlugin::new_plugin() to make test codes lighter
Moved definition of StubPlugin to test_plugin_helper.rb from weather_test_kou.rb
Fixed tabs
Modified to supply a string to module_eval. Supplying a block seems to be different
Read weather information from aviationweather.gov

- Take sample HTML from http://aviationweather.gov/adds/metars/?station_ids=RJAA&std_trans=translated&chk_metars=on&hoursStr=most+recent+only&submitmet=Submit
- Adopt to the HTML table
Read timestamp of weather data
Parse temperature (and hopefully other values with a unit)

- Broaden regexp to match value and unit sequence
Read dew point
Parse values in alternative units
Read pressure
Read speed and direction of wind
Read visiblity in km and miles
Cosmetic modification
Parse weather
Add StubPlugin::load_plugin()

The class method returns the instance of the loaded plugin
instead of its class like StubPlugin::new_plugin()
Add update_weather_url

We need to update the NOAA weather source 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
Modify @optinos not @conf when updating weather URL
Fix URL for a test