Climlab

This release mainly adds to the [documentation](http://climlab.readthedocs.io/en/latest/), including a detailed page with instructions for [contributing to climlab](http://climlab.readthedocs.io/en/latest/contributing.html).

This is associated with the forthcoming release of a meta-description paper in [Journal of Open Source Software](http://joss.theoj.org).

This release brings a new simplified API for coupling together subcomponents of a model.

There is now a method `climlab.couple()` that accepts a list of processes and returns a parent model with the given subprocesses nested inside it.

This is considered a beta feature for now and is not really documented. It partially addresses 65

Also included is a new `SimpleAbsorbedShortwave` class for energy balance models, and numerous bug fixes.

This release has some under-the-hood improvements to the Fortran builds that will let us build properly for a wider variety of platforms (including Windows / Python 3).

With thanks to xoviat

This is an experimental release with an improved build scheme. This release is really just to test the automated build procedure on conda-forge.

This release provides

- the [Emanuel convection scheme](https://emanuel.mit.edu/problem-convective-moistening), so we can now set up and run a comprehensive single- or multi-column radiative-convective model with interactive water vapor
- support for asynchronous coupling of time-dependent components
- significant optimization of some climlab internals to speed up the runtime

No backwards-incompatible changes have been introduced.

This release brings basic integration with [xarray](http://xarray.pydata.org/en/stable/).

There are now `to_xarray()` methods for automated translation of climlab model variables into `xarray.DataArray` and `xarray.Dataset` objects. See [the new docs](http://climlab.readthedocs.io/en/latest/xarray.html).

This should simplify analysis and plotting of model output.

Deeper integration with `xarray` is planned for later releases.