Assert, Exit builtins

* Builtins for assert and exit are added
* Tests for assert are added
* file operations from previous MR are added to documents
* assert and exit are added to documents

snippets/userlib.rls

@@ -18,6 +18,20 @@
 
 ;; USERLIB
 ;; This file contains useful features that are not shipped in the STL
+;; TODO
+;; dir-path
+;; abs-path
+;; rel-path
+;; unique (make set)
+;; set add
+;; set del
+;; superset
+;; common-set
+;; make-map
+;; ins-mapping
+;; del-mapping
+;; get-mapping
+;; mapped?
 
 ;; this would be way faster as code in stl
 ;; but stl already suffers scope creep