Move deptree2dot to the support folder

Since deptree2dot and the perl requirement are completely optional, we
can move this tool to the support folder. This gives the user the option
of using it if they have perl installed, and means we do not have an
optional runtime dependency on perl.

Documentation for this tool has also been added to the support folder.

X-Gentoo-Bug: 600742
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=600742

src/Makefile

@@ -3,9 +3,5 @@
 
 SUBDIR=		test libeinfo librc rc
 
-ifeq (${MKTOOLS},yes)
-SUBDIR+= tools
-endif
-
 MK=		../mk
 include		${MK}/subdir.mk