0.3.0

As discussed in #350, Awkward arrays can no longer be used as Pandas columns. Also part of this API change (#464),

• array.tojson has been removed: use ak.to_json(array).
• array.columns has been renamed: use array.fields.
• ak.keys(array) has been renamed: use ak.fields(array). (ak.keys still exists with a "deprecated until 0.4.0" message)
• array.ndim (property) is now the dimension of the array, rather than 1 (a Pandas requirement)
• array.type has been added; it is equivalent to ak.type(array). If you had fields named "type", they will now have to be accessed as array["type"], rather than array.type.

Thanks to @reikdas, this is the first release with a formal specification for the cpu-kernels/cuda-kernels library! (The bottom layer of the 3-layer architecture, documented here.)

Furthermore, ufunc behavioral matching has been generalized (#463) to allow:

ak.behavior[np.multiply, numbers.Number, "Vector"] = scalar_multiply
ak.behavior[np.multiply, "Vector", numbers.Number] = scalar_multiply

Two mistakes were fixed in the Windows builds (#465 by @chrisburr and #467), allowing them to be used without debug-version system libraries (#430). The first of these enabled @lgray to deploy it on conda-forge!

Still built on pybind 2.4.3, though we might want to update that, especially if pybind supports the NumPy datetime dtypes.