Change `Field.__repr__` to match representation in `pystencils.fields`

repr of Field should look like

y: uint16_t[246,704,558]
x(3): float[20,40]

to match representation when using pystencils.fields

E.g.

In [3]: pystencils.fields('x: float32[20,40]')                                                                                                                                                                                                                                
Out[3]: x: float[20,40])

In [4]: pystencils.fields('x(3): float32[20,40]')                                                                                                                                                                                                                             
Out[4]: x(3): float[20,40])

pystencils/field.py

@@ -83,7 +83,7 @@ def fields(description=None, index_dimensions=0, layout=None, field_type=FieldTy
 
         Format string can be left out, field names are taken from keyword arguments.
             >>> fields(f1=arr_s, f2=arr_s)
-            [f1, f2]
+            [f1: double[20,20], f2: double[20,20]]
 
         The keyword names ``index_dimension`` and ``layout`` have special meaning, don't use them for field names
             >>> f = fields(f=arr_v, index_dimensions=1)
@@ -392,7 +392,15 @@ class Field(AbstractField):
         return self.dtype.numpy_dtype.itemsize
 
     def __repr__(self):
-        return self._field_name
+        if self.index_shape:
+            return f'{self._field_name}({",".join(str(i) for i in self.index_shape)}): ' \
+                f'{self.dtype}[{",".join(str(i) for i in self.spatial_shape)}]'
+        else:
+            return f'{self._field_name}: ' \
+                f'{self.dtype}[{",".join(str(i) for i in self.spatial_shape)}]'
+
+    def __str__(self):
+        return self.name
 
     def neighbor(self, coord_id, offset):
         offset_list = [0] * self.spatial_dimensions