Support load roles definition from JSON files

Add set_chef_roles function to load JSON files as chef-role definition.
Add "about roles" to README
Merge changes in master
Support ruby installed by rbenv on user-land (cooperate with capistrano-rbenv)
Merge branch 'cooperate-with-capistrano-rbenv' into integrated
Merge branch 'support-roles' into integrated
Install ruby and chef using chef-omnibus-installer
Merge branch 'cooperate-with-chef-omnibus-installer' into integrated
Run "rbenv rehash" after install chef-solo to generate binstubs
Merge branch 'cooperate-with-capistrano-rbenv' into integrated
Support role files

Transfering roles directory and write path configration to solo.rb.
Add feature: Chef roles auto discovery

Chef roles auto discovery appends roles of chef to run_list of each server.
This feature makes name-based relations with role of capistrano and chef's one::
- Discovering role definitions of chef from role-names of capistrano that server is assigned
- Run chef with discovered roles at each server
- Be able to play different roles of chef for each server
Merge branch 'chef_roles_auto_discovery' into integrated
Merge pull request #1 from nathanielram/integrated

Move integrated branch to master