fix doc strings

	* symbols.c, streams.c, lispcmds.c: fix doc strings (an old
	global search and replace had mangled "VALUE" -> "repv")
added a resizable heap as a separate data type

	* rep/data/heap.jl: renamed the functions and added a resizable
	heap implementation as a separate data type
fix heap/remove bug, added a few unit tests

	* rep/data/heap.jl, rep/test/autoload.jl: fix heap/remove bug,
	added a few unit tests