Set HDF5 API to closer match netCDF3

[martindurant]

Fixes #186

@rabernat , this raises the question of what to do for the backends that are implemented as simple functions, e.g., grib. Should they all be wrapped in a class of the same structure?

[martindurant]

This is how a wrapper class for grib would look:

class GribToZarr:
    def __int__(self, url, common_vars=None, storage_options=None,
                inline_threshold=100, skip=0, filter=None):
        self.url = url
        self.common_vars = common_vars or []
        self.inline_threshold= inline_threshold
        self.storage_options = storage_options or {}
        self.skip = skip
        self.filter = filter or {}

    def translate(self):
        return scan_grib(self.url, self.common_vars, self.storage_options, self.inline_threshold,
                         self.skip, self.filter)

[martindurant]

Merging this here, so that development can continue for netCDF3 without conflicts with the reformatting