add numeric type hierarchy and issubdtype as well as a set_dtype meth… (#427)

* add numeric type hierarchy and issubdtype as well as a set_dtype method to nn.Module with predicate

numeric type hierarchy and issubtype is compatible to the [numpy hierarchy](https://github.com/numpy/numpy/blob/220f0ab2c5958f9d49b9a28c69a760657b06d9b9/numpy/_core/numerictypes.py#L42).

Closes #285.

* nits in docs

* unify type category checking

* nits in docs

* nits in docs

* more docs nits

* fix callable type

---------

Co-authored-by: Awni Hannun <[email protected]>

docs/src/python/array.rst

@@ -19,7 +19,6 @@ Array
     array.ndim
     array.shape
     array.size
-    Dtype
     array.abs
     array.all
     array.any
@@ -32,7 +31,6 @@ Array
     array.cumsum
     array.diag
     array.diagonal
-    array.dtype
     array.exp
     array.flatten
     array.log

docs/src/python/data_types.rst

@@ -1,7 +1,5 @@
 .. _data_types:
 
-:orphan:
-
 Data Types
 ==========
 
@@ -56,3 +54,15 @@ The default floating point type is ``float32`` and the default integer type is
    * - ``complex64``
      - 8 
      - 64-bit complex float
+
+
+Data type are aranged in a hierarchy. See the :obj:`DtypeCategory` object
+documentation for more information. Use :func:`issubdtype` to determine if one
+``dtype`` (or category) is a subtype of another category.
+
+.. autosummary::
+   :toctree: _autosummary
+
+   Dtype
+   DtypeCategory
+   issubdtype

docs/src/python/nn/module.rst

@@ -30,6 +30,7 @@ Module
       Module.named_modules
       Module.parameters
       Module.save_weights
+      Module.set_dtype
       Module.train
       Module.trainable_parameters
       Module.unfreeze

docs/src/python/ops.rst

@@ -62,10 +62,10 @@ Operations
    identity
    inner
    isclose
-   isnan
-   isposinf
-   isneginf
    isinf
+   isnan
+   isneginf
+   isposinf
    less
    less_equal
    linspace