data types

Name	Meaning
`f8`	java primitive `double`
`f4`	java primitive `float`
`i8`	java primitive `long`
`i4`	java primitive `int`
`u4`	java primitive `int` shall be used unsigned
`i2`	java primitive `short`
`u2`	java primitive `short` shall be used unsigned
`i1`	java primitive `byte`
`u1`	java primitive `byte` shall be used unsigned

This list of data types will be extended in the future.

Little by little they should match the ones defined in Python zarr.