use HTML <sup> instead of ** for exponents

multiplied relative speed indicators by 100 for ease-of-use
added explicit recommendation of mt19937 for newbies
rand48 description: say that it requires an integral uint64_t


[SVN r7886]

libs/random

@@ -1 +1 @@
-Subproject commit 9c9de41bdf09d0083a85e8d5aca54d308fac819b
+Subproject commit 237a4172f25ab1901fc336a4fea17b2cb319728e