river: add position and dimensions rules

This commit adds position and dimensions rules for configuring
the initial position and dimensions of views.

When a view is not matched by any position rules, it is centered
in the avaliable output space matching the current behavior. If
the provided position rule places the view outside of the output,
the view's position is clamped to the output bounds (with respect
to borders).

When a view is not matched by any dimensions rules, no default
dimensions is set by the server. If the provided dimensions rule
exceeds the minimum or maximum width/height constraints of the view,
the view's width/height is clamped to the constraints.

Position and dimensions rules have no effect if a view is started
fullscreen or is not floating. A view must be matched by a float
rule in order for them to take effect.

doc/riverctl.1.scd

@@ -274,11 +274,11 @@ For example, _abc_ is matched by _a\*_, _\*a\*_, _\*b\*_, _\*c_, _abc_, and
 _\*_ but not matched by _\*a_, _b\*_, _\*b_, _c\*_, or _ab_. Note that _\*_
 matches everything while _\*\*_ and the empty string are invalid.
 
-*rule-add* [*-app-id* _glob_|*-title* _glob_] _action_ [_argument_]
+*rule-add* [*-app-id* _glob_|*-title* _glob_] _action_ [_arguments_]
 	Add a rule that applies an _action_ to views with *app-id* and *title*
 	matched by the respective _glob_. Omitting *-app-id* or *-title*
 	is equivalent to passing *-app-id* _\*_ or *-title* _\*_.
-	Some actions require an _argument_.
+	Some actions require one or more _arguments_.
 
 	The supported _action_ types are:
 
@@ -298,6 +298,15 @@ matches everything while _\*\*_ and the empty string are invalid.
 	  with make: _HP Inc._, model: _HP 22w_, and serial: _CNC93720WF_, the
 	  identifier would be: _HP Inc. HP 22w CNC93720WF_. If the make, model, or
 	  serial is unknown, the word "Unknown" is used instead.
+	- *position*: Set the initial position of the view, clamping to the
+	  bounds of the output. Requires x and y coordinates of the view as
+	  arguments, both of which must be non-negative. Applies only to new views.
+	- *dimensions*: Set the initial dimensions of the view, clamping to the
+	  constraints of the view. Requires width and height of the view as
+	  arguments, both of which must be non-negative. Applies only to new views.
+	- *fullscreen*: Make the view fullscreen. Applies only to new views.
+	- *no-fullscreen*: Don't make the view fullscreen. Applies only to
+	  new views.
 
 	Both *float* and *no-float* rules are added to the same list,
 	which means that adding a *no-float* rule with the same arguments
@@ -323,10 +332,14 @@ matches everything while _\*\*_ and the empty string are invalid.
 	wishes of the client and may start the view floating based on simple
 	heuristics intended to catch popup-like views.
 
+	If a view is started fullscreen or is not floating, then *position* and
+	*dimensions* rules will have no effect  A view must be matched by a *float*
+	rule in order for them to take effect.
+
 *rule-del* [*-app-id* _glob_|*-title* _glob_] _action_
 	Delete a rule created using *rule-add* with the given arguments.
 
-*list-rules* *float*|*ssd*|*tag*
+*list-rules* *float*|*ssd*|*tag*|*position*|*dimensions*
 	Print the specified rule list. The output is ordered from most specific
 	to least specific, the same order in which views are checked against
 	when searching for a match. Only the first matching rule in the list