Now you can open the currently selected item in a vertical split or a
horizontal split. The completion callback must support the current
actions.
There is also a bit of testing in here. The vim mock has been refactored
and split out so we can use it multiple tests.
Passes values by reference when sorting to reduce memory copying. The
main saving on this is preventing copying of the large vector of files
getting passed into the `sort` function and then copying each item in
the vector in the for. This results in about a 27% performance gain
reducing the full benchmark of the kubernetes benchmark by 7.89 sec
Before
| Name | Total | Average | Min | Max |
| ---------------------------- | ------------- | ------------- | ------------- | ------------- |
| ivy_match(file.lua) 1000000x | 02.351614 (s) | 00.000002 (s) | 00.000002 (s) | 00.000042 (s) |
| ivy_files(kubernetes) 100x | 32.704256 (s) | 00.327043 (s) | 00.289397 (s) | 00.344413 (s) |
After
| Name | Total | Average | Min | Max |
| ---------------------------- | ------------- | ------------- | ------------- | ------------- |
| ivy_match(file.lua) 1000000x | 02.353386 (s) | 00.000002 (s) | 00.000002 (s) | 00.000049 (s) |
| ivy_files(kubernetes) 100x | 24.809576 (s) | 00.248096 (s) | 00.203167 (s) | 00.270263 (s) |
