Add working tests for pinning and unpinning functionality
Add working tests for pinning and unpinning functionality

Also update the note on how to run the tests using the reduced vimrc.

The sleep commands are required for the pinning and unpinning tests to
work reliabily. I don't understand why though. For reference see the
following commit with a preferred approach to the tests that
unfortunately I couldn't get to work:
bae7514fadc0e721f38d2a8af63980a665fa1aa6

References #57

sanchon/simplenote.vim,sanchon/simplenote.vim,mrtazz/simplenote.vim,mrtazz/simplenote.vim,yuex/simplenote.vim,kidpixo/simplenote.vim