Fix RuboCop offenses

- Remove redundant `self`
- Use single-quote strings
- Add space for operator and comma
- Prefer one line `if` statement
- Use ascii comments
Update documentation of `TermApp::Terminal`

- `lines`, `columns`
- `current_user`, `current_board`
- `#clrtoeol`
- `#mvaddstr`
- `#getyx`
- `#mvgetnstr`
- `#erase_body`
- `#erase_all`
- `#getmaxyx`
- `#print_block`
- `#print_header`
- `#print_footer`
Merge pull request #64 from yous/patch-rubocop

Fix RuboCop offenses
Merge pull request #65 from yous/patch-documentation

Update documentation of `TermApp::Terminal`