added tools to library browser

mainly so other forks of Snap! (especially Beetleblocks) can use blocks
like FOR

libraries/LIBRARIES

@@ -1,3 +1,4 @@
+tools.xml	Tools	Standard library of powerful blocks (for, map, etc.)
 iteration-composition.xml	Iteration, composition	Traditional loop constructs (while, until, etc.) plus the Lisp "named let" (a generalization of FOR) plus functional iteration (repeated invocation of a function) and function composition.
 list-utilities.xml	List utilities	Some standard functions on lists (append, reverse, etc.)
 stream-tools.xml	Streams (lazy lists)	A variation on the list data type in which each list item aren't computed until it's needed, so you can construct million-item lists without really taking up all that time or memory, or even infinite-sized lists.  (A block that reports all the prime numbers is included as an example.)