Add documentation for immediates with type bool.

This makes the documentation for the new bconst instruction more complete.

docs/langref.rst

@@ -265,6 +265,13 @@ indicate the different kinds of immediate operands on an instruction.
     A 64-bit immediate floating point number in the IEEE 754-2008 binary64
     interchange format. All bit patterns are allowed.
 
+.. type:: bool
+
+    A boolean immediate value, either false or true.
+
+    In the textual format, :type:`bool` immediates appear as 'false'
+    and 'true'.
+
 .. type:: intcc
 
     An integer condition code. See the :inst:`icmp` instruction for details.

lib/cretonne/meta/base/immediates.py

@@ -49,7 +49,7 @@ ieee64 = ImmediateKind('ieee64', 'A 64-bit immediate floating point number.')
 #:
 #: This type of immediate boolean can interact with SSA values with any
 #: :py:class:`cretonne.BoolType` type.
-boolean = ImmediateKind('boolean', 'An immediate boolean.',
+boolean = ImmediateKind('bool', 'An immediate boolean.',
                         rust_type='bool')
 
 #: A condition code for comparing integer values.