What type of PR is this? (check all applicable)

• Refactor
• Feature
• Bug Fix
• Optimization
• Documentation Update
• Other: Replace this with a description of the type of this PR

Description

A new set of configuration options are added to allow to set corner radii
separately. For motivation see #2294.

Additionally to the already present radius and radius-{bottom,top}
radius-{bottom,top}-{left,right} configuration options are added. If not
present they fall back to radius-bottom, radius-top or ultimately radius
to preserve current semantics.

Related Issues & Documents

This implements #2294.

Documentation (check all applicable)

• This PR requires changes to the Wiki documentation (describe the changes)
  See provided patch below (to be applied to Home → Configuration).
• This PR requires changes to the documentation inside the git repo (please add them to the PR).
• Does not require documentation changes

--- configuration_old.md	2020-12-13 16:33:34.677959229 +0100
+++ configuration_new.md	2020-12-13 16:38:17.929004974 +0100
@@ -201,8 +201,10 @@
 ; Note: This shouldn't be used together with border-size because the border 
 ; doesn't get rounded. For this to work you may also need to enable 
 ; pseudo-transparency or use a compositor like compton.
-; Individual top/bottom values can be defined using:
-;   radius-{top,bottom}
+; Individual top/bottom-left/right values can be defined using:
+;   radius-{top,bottom}-{left,right}
+; In case radius-{top,bottom} is provided, it is applied to {left,right}. If
+; just radius is provided its value is used for all corners.
 radius = 0.0
 
 ; Under-/overline pixel size and argb color