Esmf-regrid

This release added the ability to regrid data stored on a UGRID mesh.

Added

- [PR31](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/31)
[PR32](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/32)
[PR36](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/36)
[PR39](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/39)
[PR46](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/46)
[PR55](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/55)
[PR96](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/96)
Added the unstructured regridders `GridToMeshESMFRegridder` and
`MeshToGridESMFRegridder`.
[stephenworsley](https://github.com/stephenworsley) with extensive review
work from [abooton](https://github.com/abooton) and
[jamesp](https://github.com/jamesp) with benchmarking help from
[trexfeathers](https://github.com/trexfeathers)
- [PR130](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/130)
[PR137](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/137)
Added functions for saving of the unstructured regridders.
[stephenworsley](https://github.com/stephenworsley)
- [PR155](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/155)
Enabled Sphinx and RTD for automatically rendering the API.
[trexfeathers](https://github.com/trexfeathers)

The major change with this version was the addition of the ability to
regrid curvilinear grids (i.e. grids with 2D arrays of coordinates).

Added
- [PR125](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/125)
Added support for curvilinear grids, i.e. cubes with 2D lat/lon coords.
[stephenworsley](https://github.com/stephenworsley)
- [PR124](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/124)
Improved generation of benchmark data to allow data to be generated from
a common version/environment.
[trexfeathers](https://github.com/trexfeathers)

The major change in this version is the addition of lazy regridding.
This defers the calculation of regridding to the realisation of the data
when the data is a dask array. Calculations may be parallelised via dask.

Added
- [PR80](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/80)
Added support for lazy regridding, this showed an improvement in the
performance of the regridding benchmarks.
[stephenworsley](https://github.com/stephenworsley)
- [PR79](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/79)
Added support for benchmarks on the CI.
[trexfeathers](https://github.com/trexfeathers)
- [PR98](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/98)
Added benchmarks for regridding with realised data.
[stephenworsley](https://github.com/stephenworsley)
- [PR100](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/100)
Added benchmarks for regridding with lazy data.
[stephenworsley](https://github.com/stephenworsley)

Fixed
- [PR92](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/92)
Fixed an issue with directory naming. [lbdreyer](https://github.com/lbdreyer)
- [PR83](https://github.com/SciTools-incubator/iris-esmf-regrid/pull/83)
Added missing docstrings. [stephenworsley](https://github.com/stephenworsley)