Support for unsigned data

[forman]

The "old" NetCDF 3 format doesn't have explicit support for unsigned integer types and therefore a recommendation/convention exists to set the variable attribute _Unsigned='true', see NetCDF docs, section Unsigned Data.

Are there any plans to interpret the _Unsigned attribute?

I'd really like to help out, but I fear I still don't know enough about dask to provide an efficient PR for that.

My workaround is to manually convert the variables in question which are of type int8, same data as mentioned in #1576:

unsigned_var = signed_int8_var & 0xff

which results in an int16, which is ok but still 1 byte more than the desired uint8.

[jhamman]

Didn't #1453 add this?

[forman]

Yes, so this is a duplicate of #1444, sorry!

When can we expect 0.9.7 with the fix?

[shoyer]

We are trying to get everything together for a big 0.10 release, so it will be a bit longer. I don't have a timeframe yet, but hopefully in a week or two!