* Add `Object:{is_class_of,is_extended_by}` to check inverse relationships
* Make tab scrolling more flexible
This adds tab scrolling commands and connects them to mouse scroll
events.
This way scrolling behavior can be customized more easily.
For example an alternative behavior could be:
```lua
keymap.add({
["wheelup"] = "root:switch-to-hovered-previous-tab",
["wheeldown"] = "root:switch-to-hovered-next-tab"
})
```
Currently some plugins had/have issues with predicates that check
if active view is a docview to perform certain operations like draw
in the case of minimap or lineguide. Since is() was checking the
entire inheritance tree it was returning true for views that inherit
from the same parent, which caused CommandView to be matched along
DocView, etc... This change does the following to solve the issue:
* Make Object:is() only match the top level parent of the object which
is more in line with what one would expect from a method named 'is'.
* Introduces Object:extends() which keeps the same functionality that
Object:is() offered before.
George Sokianos
Luke aka SwissalpS
Guldoman
jgmdev
Francesco Abbate
rxi