Added ability to set a default emoji size from the collection settings

Closes #1.

README.md

@@ -1,6 +1,6 @@
 # Emoji for Pencil
 
-Twitter Emoji as a Pencil stencil collection - drag-and-drop emoji into your mockups! :thumbsup:
+Twitter Emoji as a [Pencil](https://github.com/prikhi/pencil) stencil collection - drag-and-drop emoji into your mockups! :thumbsup:
 
 *Check out my other stencil collections for Pencil at [nathanielw.github.io/pencil-stencils](http://nathanielw.github.io/pencil-stencils/)*
 
@@ -12,6 +12,9 @@ Twitter Emoji as a Pencil stencil collection - drag-and-drop emoji into your moc
 ### Updating
 Right-click on the collection in Pencil's sidebar and choose _Uninstall this collection_ before repeating the installation steps.
 
+### Using
+Drag-and-drop emoji from the _Collections_ panel onto your mockups. Easy. If you want to change the default emoji size, right-click on the collection in the _Collections_ panel, select _Collection settings_ and enter the desired size (it's `16,16` by default).
+
 ## Generating the Collection
 - Clone this repo with the `--recursive` flag to include submodules. (or just clone it normally then `git submodule init` and `git submodule update`)
 - Run the `generate-xml.py` script (tested with Python 3.4).

stylesheet.xsl

@@ -16,6 +16,11 @@
         
Source code for generating this stencil collection can be found at https://github.com/nathanielw/Emoji-for-Pencil and is licensed under the MIT License."
         author="Emoji graphics by Twitter used under CC-BY 4.0. Pencil Stencil by Nathaniel Watson (nwatson.nz)"
         url="https://github.com/nathanielw/Twemoji-for-Pencil">
+            <Properties>
+                <PropertyGroup name="Collection settings">
+                    <Property name="size" displayName="Default emoji size (width,height)" type="PlainText">16,16</Property>
+                </PropertyGroup>
+            </Properties>
 
             <xsl:apply-templates/>
         </Shapes>
@@ -27,7 +32,7 @@
         <Shape id="{./@id}" displayName="{./@name}" icon="{./@icon}">
             <Properties>
                 <PropertyGroup>
-                    <Property name="box" type="Dimension" p:lockRatio="true">16,16</Property>
+                    <Property name="box" type="Dimension" p:lockRatio="true"><E>$$size</E></Property>
                 </PropertyGroup>
             </Properties>