bundle gem airenv
Adds collaborator's info into gemspec.
Adds command-line system using thor
generate rspec template

bundle gem airenv -t
Adds guard env
Adds pry
Adds SdkDescription
Adds SdkDescription#id and #digest
Adds Airenv::Sdk class
Fixes version commnad description
Adds automatic task loader
Adds version parser into Sdk class
Adds Fetch command - not work
Implements fetch command
Adds configuration system
Modifies parsing SdkDescription from fetched archive
Adds use command
Adds install command
Adds init command
Fixes some bugs