Refactoring to use class folder, better examples.m, ability to change…

… grouping between layers

- Switched from a monolithic gramm.m file to a @gramm class folder with
separate files for all the methods
- examples.m is now a proper how-to, and gives good results with
matlab’s publish(). Published version is in the html folder
- With the update() methods, there is now a proper way to have
different groupings for different geom_ and stat_layers
- Support for categorical variables in facet_grid() and facet_wrap()

@gramm/axe_property.m

@@ -0,0 +1,17 @@
+function obj=axe_property(obj,varargin)
+% axe_property Add a matlab axes property to apply to all subplots
+%
+% Example syntax: gramm_object.axe_property('ylim',[0 1])
+% Arguments are given as a name,value pairs. The accepted
+% arguments are the same as in matlab's own set(gca,'propertyname',propertyvalue)
+
+if mod(nargin-1,2)==0
+    for obj_ind=1:numel(obj)
+        for k=1:2:length(varargin)
+            obj(obj_ind).axe_properties=vertcat(obj(obj_ind).axe_properties,{varargin{k},varargin{k+1}});
+        end
+    end
+else
+    error('Arguments of axe_property() must be given as ''name'',value pairs')
+end
+end