Gemfile: depend on Pry 0.10 and greater
WhenStartedHook: remove rubocop violations

I really like that it suggested me to use `next`.
Add .rubocop.yml and .rubocop_todo.yml
Remove some offences of Style/LineLength cop
Config: improve comments
WhenStartedHook: set theme_options to an empty hash

Fixes #41 (Fix error message when execute `pry -f`)