Add low-level allocation creation functions

Bug: 23535985

Create spec for rs_allocation_create.rsh that'll have functions
to create Elements, Types and Allocations from a Script.

Add this new header to scriptc/rs_core.rsh.

Change-Id: If64fbe8e5ddce11952563d40a12b234ebae5c386
diff --git a/api/generate.sh b/api/generate.sh
index 55d3f04..b569f67 100755
--- a/api/generate.sh
+++ b/api/generate.sh
@@ -31,7 +31,7 @@
 #    This can be manually changed when cut&pasting the snippet into guide_toc.cs.
 # 3. rsIs/Clear/SetObject is documented in rs_object_info but also found in rs_graphics.
 #    The latter must appear after the former.
-./generator rs_core.spec rs_value_types.spec rs_object_types.spec rs_convert.spec rs_math.spec rs_vector_math.spec rs_matrix.spec rs_quaternion.spec rs_atomic.spec rs_time.spec rs_allocation_data.spec rs_object_info.spec rs_for_each.spec rs_io.spec rs_debug.spec rs_graphics.spec
+./generator rs_core.spec rs_value_types.spec rs_object_types.spec rs_convert.spec rs_math.spec rs_vector_math.spec rs_matrix.spec rs_quaternion.spec rs_atomic.spec rs_time.spec rs_allocation_create.spec rs_allocation_data.spec rs_object_info.spec rs_for_each.spec rs_io.spec rs_debug.spec rs_graphics.spec
 
 rm generator