ODL 0.5.0

This release features a new important top level class Functional that is intended to be used in optimization methods.
Beyond its parent Operator, it provides special methods and properties like gradient or proximal which are useful in advanced smooth or non-smooth optimization schemes.
The interfaces of all solvers in odl.solvers have been updated to make use of functionals instead of their proximals, gradients etc. directly.

Further notable changes are the implementation of an as_writable_array context manager that exposes arbitrary array storage as writable Numpy arrays, and the generalization of the wavelet transform to arbitrary dimensions.

See the detailed release notes for a complete list of changes.