added support for HTML5 placeholder attribute
feature: asynchronous callback to JavaScript
• previously when a Ruby callback (proc) finished, the last value ws sent to JavaScript with the chance that a synchronous JavaScript callback would use that return value.
• for being able to to asynchronous tasks we need to explicitely specify which value to return, using a ne method `Dialog.return`
• after a proc has finished, the next message is allowed to be sent, in any case (now public method `AE.Bridge.nextMessage`).
Fix for wrong initial dialog size 
• if no specific size was set with `set_size`, it would display in 250px or the min/max limit. Now the initial dialog size is always set to the given arguments (so SketchUp can't override it ith values from the registry).
moved requirement
small changes
• platform detection
• wrong order of size/position in dialog initialization
• renamed callback `update_options`
• options dialog centered
Fix: unescaped regular expression caused errors with some special characters in search terms
Change: arguments for adding command/hash now in any order
addition: new `get_all` method
include icon path for generating hash code, to ensure it is unique 
(if two commands have the same name and description)
indentation
replaced image selector by class name
minor change and version number 1.0.8