add compare_docs task
add octokit gem
Merge pull request #126 from melborne/compare-docs-task

add compare_docs task
add thor tasks for get diffs
fix task name to dir_diff
use print instead of puts to avoid thread problem
accept dot(.) as current direcotry
fix removed files output
ensure arg passing onto thread
Merge pull request #129 from melborne/task-by-thor

add thor tasks for get diffs related #122