Updated function reference

Author: orbingol

FUNCTION_REFERENCE.md

@@ -21,12 +21,7 @@
 * api_make_torus
 * api_apply_transf
 * api_remove_transf
-* api_unite
-* api_intersect
-* api_subtract
-* api_imprint
 * api_sheet_from_ff
-* api_boolean_chop_body
 
 ## Entity
 
@@ -48,7 +43,6 @@
 * SPHERE
 * SPLINE
 * TORUS
-* surface
 
 ## Geometric Atoms
 
@@ -130,3 +124,17 @@
 ### Functions
 
 * spa_unlock_products
+
+## Booleans
+
+### Enums
+
+* NDBOOL_KEEP
+
+### Functions
+
+* api_unite
+* api_intersect
+* api_subtract
+* api_imprint
+* api_boolean_chop_body