Added .mata sample for Stata.

Source: http://www.stata.com/help.cgi?m1_first

samples/Stata/tanh.mata

@@ -0,0 +1,8 @@
+numeric matrix tanh(numeric matrix u)
+{
+		numeric matrix  eu, emu
+
+		eu = exp(u)
+		emu = exp(-u)
+		return( (eu-emu):/(eu+emu) )
+}