created strawman viewmodel class, added get method (replaces standalone get() function)
implemented Viewmodel$set
implement Viewmodel$register and Viewmodel$unregister
implemented Viewmodel$clearCache
moved ractive._cache to ractive.viewmodel.cache
deps belong to viewmodel
implement Viewmodel$adapt (replaces adaptIfNecessary)
linting
moved _changes, _evaluators, _computations from ractive to viewmodel
moved Computation.js and associated modules
move keypath capturing logic to viewmodel
Merge pull request #804 from ractivejs/viewmodel

Viewmodel