Living Style Guide: Document button size modifiers

Reorganise button documentation.

[ci skip]

Signed-off-by: Alex Coles <alex@alexbcoles.com>

app/assets/stylesheets/content/_buttons.md

@@ -1,21 +1,42 @@
 # Buttons
 
-```
-<a href="#" class="button">Click me</a>
-<a href="#" class="button -highlight">Click me</a>
-```
+## Default buttons
 
 ```
 <input type="submit" class="button" value="Submit me"/>
+<a href="#" class="button">Click me</a>
 <input type="submit" class="button" value="Do not submit" disabled />
+
 ```
 
+## Highlight buttons
+
 ```
 <input type="submit" class="button -highlight" value="Submit me"/>
+<a href="#" class="button -highlight">Click me</a>
 <input type="submit" class="button -highlight" value="Do not submit" disabled />
 ```
 
+## Active (depressed) buttons
+
 ```
 <input type="submit" class="button -active" value="Submit me"/>
+<a href="#" class="button -active">Click me</a>
 <input type="submit" class="button -active" value="Do not submit" disabled />
 ```
+
+## Button sizes
+
+```
+<button class="button -tiny">Tiny</button>
+<button class="button -small">Small</button>
+<button class="button">Default</button>
+<button class="button -large">Large</button>
+```
+
+## Expanded buttons
+
+```
+<button class="button -expand">Expanded button</button>
+<a href="#" class="button -expand">Expanded button as link</a>
+```