Add some convinience methods

Add Slice() sink (fixes bitfield#47)

* Add Slice() sink (fixes bitfield#47)

* Add test with empty pipe

* Apply suggestions from code review

Co-Authored-By: John Arundel <john@bitfieldconsulting.com>

* Not using type as variable name

* Using cmp to deep compare

* Not testing ListFiles in the test method for SliceSink

* Remove examples/visitors/go.sum who should not be commited

* An empty pipe should return an empty Slice

* Better example for Slice

* Ignore all go.sum

Co-authored-by: John Arundel <john@bitfieldconsulting.com>

* use cmp.diff when printing error

* Remove comma in doc

* Move Slice after SHA256

* Edit comments

* Adding trailing blank line:

* Single line with embeded new lines

* Code style

* Range over pids

* Code style

* Using EachLine to split on each lines

* Slice is supposed to be after SHA256

* Change order of params in cmp.Equal

* Better explanation in test

* typo

* Better example who don't use system specific command

* still an order problem

* Order problem

* Add comment to the example for slice

* Move the test to a t.Run format

* Change order for cmp.Equal

* Add example file

* Tweaks to SliceSink

Co-authored-by: John Arundel <john@bitfieldconsulting.com>
Co-authored-by: Thomas Poignant <thomas.poignant@adevinta.com>

Change SHA256Sum to not read the whole pipe into memory (bitfield#50)

Reorder alphabetically

Add Findfiles func to find files recursively (bitfield#36)

Merge pull request bitfield#44 from bitfield/execforeach

Add ExecForEach()

Merge pull request bitfield#43 from bitfield/concat_continue

Have Concat skip errors (fixes bitfield#26)

Merge pull request bitfield#42 from bitfield/better_exec

Fix Exec to handle quotes

Fix race condition on stdout in tests

Merge pull request bitfield#31 from bitfield/feature/path-filters

Add Basename and Dirname filters