Start adding spec filters for language specs
Update class language specs to use filters
Move class variables specs to filters
Initial Module#const_missing implementation and specs
Use OPAL_SPEC_DIR ENV var for specific test convenience
Make Native a class (not module) to wrap objects
Native now inherits from BasicObject instead of Object
Stop allocation a new function on method missing - reuse same one
remove some pending
add rake task
Merge branch 'feature' of git://github.com/fntzr/opal
opal/native is now included in opal.js by default
Initial implementation of Native#[]
Add 'observer' from stdlib, with all specs from rubyspec
Support sending arguments with Native#method_missing.

method_missing is used to forward calls to the native javascript object
being wrapped by the instance of Native. Each ruby arg is simply passed
into the function call. The context of each call is also checked to be
the native object.
Add implementation (and specs) of Native#==.

Two native instances are equal if their two native objects are strictly
equal in javascript.
Support setting properties via Native#method_missing
Add Native.global as reference to global javascript context
Native#method_missing wraps returned objects in Native.

This allows simple chaining. This commit also refactors the specs for
method_missing to group them into their logical operations.
Seperate corelib and stdlib into their own directories