Permit use of codec registry with N5Store (#577)

* enable arbitrary compressors for N5Store

* enable arbitrary compressors for N5Store creation

* pep8

* don't mutate the config dict

* pep8

Author: d-v-b

zarr/n5.py

@@ -461,7 +461,7 @@ def compressor_config_to_n5(compressor_config):
 
     else:  # pragma: no cover
 
-        raise RuntimeError("Unknown compressor with id %s" % codec_id)
+        n5_config.update({k: v for k, v in compressor_config.items() if k != 'type'})
 
     return n5_config
 
@@ -513,7 +513,7 @@ def compressor_config_to_zarr(compressor_config):
 
     else:  # pragma: no cover
 
-        raise RuntimeError("Unknown compressor with id %s" % codec_id)
+        zarr_config.update({k: v for k, v in compressor_config.items() if k != 'type'})
 
     return zarr_config