Move ValueType into a new cdsl top-level module.

We want to separate the Python classes that make up the DSL used to
define the Cretonne language from the concrete definitions.

- cdsl.types defines the ValueType class hierarchy.
- base.types defines the concrete types.

lib/cretonne/meta/base/__init__.py

@@ -0,0 +1 @@
+"""Definitions for the base Cretonne language."""

lib/cretonne/meta/base/types.py

@@ -0,0 +1,38 @@
+"""
+The base.types module predefines all the Cretonne scalar types.
+"""
+from __future__ import absolute_import
+from cdsl.types import ScalarType, IntType, FloatType, BoolType
+
+#: Boolean.
+b1 = ScalarType(
+        'b1', 0,
+        """
+        A boolean value that is either true or false.
+        """)
+
+b8 = BoolType(8)    #: 8-bit bool.
+b16 = BoolType(16)  #: 16-bit bool.
+b32 = BoolType(32)  #: 32-bit bool.
+b64 = BoolType(64)  #: 64-bit bool.
+
+i8 = IntType(8)     #: 8-bit int.
+i16 = IntType(16)   #: 16-bit int.
+i32 = IntType(32)   #: 32-bit int.
+i64 = IntType(64)   #: 64-bit int.
+
+#: IEEE single precision.
+f32 = FloatType(
+        32, """
+        A 32-bit floating point type represented in the IEEE 754-2008
+        *binary32* interchange format. This corresponds to the :c:type:`float`
+        type in most C implementations.
+        """)
+
+#: IEEE double precision.
+f64 = FloatType(
+        64, """
+        A 64-bit floating point type represented in the IEEE 754-2008
+        *binary64* interchange format. This corresponds to the :c:type:`double`
+        type in most C implementations.
+        """)