Add Local model for site-specific projections

[Greg Munday (gregrmunday)]

Does what it says on the tin! Same use as the Spatial projections class but the user provides a set of site and lat/lons.

Closes #66

[Hemant Khatri (hmkhatri)]

Greg Munday (@gregrmunday) thanks for the pull request. Need to think about interpolation around boundaries. I am working on land mask issue and interpolation with land mask. Maybe better to merge that first and then review this pull request.

[Greg Munday (gregrmunday)]

Greg Munday (Greg Munday (@gregrmunday)) thanks for the pull request. Need to think about interpolation around boundaries. I am working on land mask issue and interpolation with land mask. Maybe better to merge that first and then review this pull request.

Sounds good to me! I'll have a think about how we can handle this too. I feel like we should think carefully about this and not being too prescriptive with flags/warnings/exceptions, but somehow still return something sensible if they give us tricky grid-boxes...

[Greg Munday (gregrmunday)]

Hemant Khatri (@hmkhatri) This is ready for review! I've handled propagating the masking slightly differently than you, but made sure to always pick the "nearest" during interpolation and then I've updated both the Local and Spatial models to sum using skipna=False, just to make sure the final total sea-level at the coast isn't missing the thermal expansion component.

See the tutorial notebook on how to use the module.