[ENH] Predictions: Show errors

[janezd]

Issue

Closes #5971.

Description of changes

Add columns with errors for each predictor.

Please comment on functionality and interface. Checking and tests will come afterwards.

Try it on housing and heart disease; errors on iris are too small.

Includes

• Code changes
• Tests
• Documentation

[ajdapretnar]

I fully approve this functionality! It enables selecting the most underpredicted, overpredicted and best predicted instances and showing them in the scatter plot. I also like the many options for error computation, discretely placed at the top.

[codecov]

Codecov Report

Merging #6012 (def1d61) into master (6d95493) will increase coverage by 0.01%.
The diff coverage is 96.61%.

@@            Coverage Diff             @@
##           master    #6012      +/-   ##
==========================================
+ Coverage   86.60%   86.61%   +0.01%     
==========================================
  Files         315      315              
  Lines       67317    67479     +162     
==========================================
+ Hits        58297    58447     +150     
- Misses       9020     9032      +12     

[lanzagar]

column was already divided by 2 above (line 1271)!

I must say, there is quite a lot of %2==1 and //2 in this file... :)

[janezd]

column was already divided by 2 above (line 1271)!

It is disturbing that (seemingly thorough) tests didn't catch this because they used only a single predictor... :(

I fixed this and modified the tests to use two predictors.

I must say, there is quite a lot of %2==1 and //2 in this file... :)

Apparently (at least) one too many. :)