Remove dtype in favor of DataType

This supersedes e6bed74 in
apr2022-prune branch (PR #178).

There was a new usage of dtype.bifrost2string in ndarray.py, which
wasn't part of the apr2022-prune branch.  I think (?) I worked around
it correctly using the enum.

We also discovered and fixed a NameError bug in DataType.

python/bifrost/DataType.py

@@ -129,7 +129,7 @@ def __init__(self, t: Optional[Union[str,_th.BFdtype_enum,_bf.BFdtype,"DataType"
             self._veclen = 1 # TODO: Consider supporting this as part of string
         elif isinstance(t, (_th.BFdtype_enum, _bf.BFdtype)): # Note: This is actually just a c_int
             t = _th.BFdtype_enum(t).value
-            self._nbit = t & BF_DTYPE_NBIT_BITS
+            self._nbit = t & _bf.BF_DTYPE_NBIT_BITS
             is_complex = bool(t & _bf.BF_DTYPE_COMPLEX_BIT)
             self._kind = KINDMAP[t & _bf.BF_DTYPE_TYPE_BITS]
             if is_complex:

python/bifrost/ndarray.py

@@ -40,9 +40,8 @@
 import ctypes
 import numpy as np
 from bifrost.memory import raw_malloc, raw_free, raw_get_space, space_accessible
-from bifrost.libbifrost import _bf, _check, _space2string
+from bifrost.libbifrost import _bf, _th, _check, _space2string
 from bifrost import device
-from bifrost.dtype import bifrost2string
 from bifrost.DataType import DataType
 from bifrost.Space import Space
 from bifrost.libbifrost_generated import struct_BFarray_
@@ -171,7 +170,7 @@ def __new__(cls, base=None, space=None, shape=None, dtype=None,
                 shape = list(base.shape)[:ndim]
                 strides = list(base.strides)[:ndim]
                 space = _space2string(base.space)
-                dtype = bifrost2string(base.dtype)
+                dtype = _th.BFdtype_enum(base.dtype)
 
                 return ndarray.__new__(cls,
                     space=space,