conda package

[pmav99]

we should have a conda package, too.

This is needed e.g. for inspectds

[tomsail]

tasks for this issue:

• [x] create latest tag (and fix #24 and #35 along the way)
• [ ] create xarray-selafin-feedstock repo and build a package locally
• [ ] create a fork on conda-forge to release the conda version of package