Add homepage URI
Use gem_tasks instead of use gem_helper and implement tasks
Use #program_name
Modify gem description slightly
Move version number from gemspec file to class constnt
Add recommendation of installing redcarpet
Remove description from usage
Align argument description following gem rdoc
Slightly change variable names
Add description about directory documentation generated
Add desc about directory to summary
[REFACTORING]Extract generating yardoc proc to a method
Remove unneccessary declaration
Output directory docs generated at last