Constructor to create DataArrays from scratch
Switch DataArray to use __init__ instead of __new__

__new__ is no longer necessary because we can consolidate all the initailization
in a single method, and no longer need to warn about direct usage.
Copy dataset when creating a DataArray?

This would make it safe to modify a DataArray in-place.
Faster Dataset.copy() by avoiding validation
New data_array.Indexes object allows for name and int based indexing
DataArray constructor now infers arguments if data is a self-described array
Coordinate.as_index now includes the name
Infer indexes from pandas objects when constructing a DataArray
Merge pull request #149 from shoyer/data-array-constructor

Data array constructor