Add notes about mpreal support and regenerate docs.

Also add missing config file.

[SVN r67283]

libs/math

@@ -1 +1 @@
-Subproject commit 309e2c3ec56b05901b3edbbfd31f09d54d10d9d2
+Subproject commit 79a91880f4628699838681e05896af63462bc572