Update access to variables

See merge request !4

As we actually have 10 tests instead of 9, just one was overwriting
another one.

BUGFIX: Allow Python < 3.5 to work

See merge request !3

Until we migrate deprecated copyRealFile we need to stick to a lower
version.

As run method was introduces in version 3.5, the plugin did not work in
lower Python versions. We therefore replaced the call with a older high
level API.

Feature/add tests

See merge request !1

* As neovim will use the same object we can't save file specific
  information in self.
* Also no locking is required