Change "after" methods in tests to "teardown"

Simplecov was showing these two lines weren't running in the test suite.
Minitest expects "setup"/"teardown", not "setup"/"after".
Add .DS_Store to gitignore
Ignore .ruby-version
WIP: testing RemoteInterface

- add tests for RemoteInterface#read_command
  - indirectly tests RemoteInterface#readline
- comments for RemoteInterface#close expectations
- comments for RemoteInterface#confirm expectations