[IMP] implement .alike suffix on props

It is common in Owl components to have anonymous function as props.
However, since each rendering create a different (but equivalent)
closure, Owl will consider the props different, so will update the child
component, but this is (often) not necessary.

This commit will help reduce the problem by introducing a new `.alike`
prop suffix, that will let Owl know that each version of that specific
prop should be considered the same, so, will be ignored by the props
comparison code.

closes #1360

doc/reference/props.md

@@ -4,6 +4,7 @@
 
 - [Overview](#overview)
 - [Definition](#definition)
+- [Props comparison](#props-comparison)
 - [Binding function props](#binding-function-props)
 - [Dynamic Props](#dynamic-props)
 - [Default Props](#default-props)
@@ -56,6 +57,47 @@ the `props` object contains the following keys:
 - for `ComponentA`: `a` and `b`,
 - for `ComponentB`: `model`,
 
+## Props comparison
+
+Whenever Owl encounters a subcomponent in a template, it performs a shallow
+comparison of all props. If they are all referentially equal, then the subcomponent
+will not even be updated. Otherwise, if at least one props has changed, then
+Owl will update it.
+
+However, in some cases, we know that two values are different, but they have the
+same effect, and should not be considered different by Owl. For example, anonymous
+functions in a template are always different, but most of them should not be
+considered different:
+
+```xml
+<t t-foreach="todos" t-as="todo" t-key="todo.id">
+  <Todo todo="todo" onDelete="() => deleteTodo(todo.id)" />
+</t>
+```
+
+In that case, one can use the `.alike` suffix:
+
+```xml
+<t t-foreach="todos" t-as="todo" t-key="todo.id">
+  <Todo todo="todo" onDelete.alike="() => deleteTodo(todo.id)" />
+</t>
+```
+
+This tells Owl that this specific prop should always be considered equivalent
+(or, in other words, should be removed from the list of comparable props).
+
+Note that even if most anonymous functions should probably be considered `alike`,
+it is not necessarily true in all cases. It depends on what values are captured
+by the anonymous function. The following example shows a case where it is probably
+wrong to use `.alike`.
+
+```xml
+<t t-foreach="todos" t-as="todo" t-key="todo.id">
+  <!-- Probably wrong! todo.isCompleted may change -->
+  <Todo todo="todo" toggle.alike="() => toggleTodo(todo.isCompleted)" />
+</t>
+```
+
 ## Binding function props
 
 It is common to have the need to pass a callback as a prop. Since Owl components
@@ -95,6 +137,9 @@ class SomeComponent extends Component {
 }
 ```
 
+The `.bind` suffix also implies `.alike`, so these props will not cause additional
+renderings.
+
 ## Dynamic Props
 
 The `t-props` directive can be used to specify totally dynamic props: