added two string functions, doc updates

Readme.md

@@ -1,15 +1,12 @@
 
 ### BUGS
 -  (read-file "nonexisting/file.csv") shows only "could not open file" - should print filename
-- error: the expression `("/usr/local/var/mlisp")` with message "cannot cast" - should add to what is casting
 - better error reporting..for example ls_dir on non existing dir should prind `pwd` dir
 
 
 
 ### TODO
 - add debug support, at least call stack
-- add stdtest - to test every functionality
-- add parenthesis coloring into linenoise
 - multiline editing (kilo editor)
 - execute system command should capture stderr
 - add some mem stats to benchmark