Update to Duktape 1.0.2
Merge pull request #1 from josh/1.0.2

Update to Duktape 1.0.2
ContextError should include the error message
Add CHANGELOG
Include README/CHANGELOG in gem
Add error subclasses for each error code
Raise an argument error for unsupported call types
Actually, TypeError
Define ContextObject class/instance
Keep ivar reference to complex object instance
Store ComplexObject in a hidden ivar:

This avoids crashing everything when bad people doing weird things.
Update CHANGELOG
Travis CI:

* Be less precise in Ruby versions
* Use sudo-less containers