Add a test for the unicode package

This massively increases .data size, possibly because loads of unused
globals are included. I'll need to investigate what's going on here. For
now, increase the RAM size for nrf chips (the nrf52 has 64kB of RAM).

arm.ld

@@ -2,7 +2,7 @@
 MEMORY
 {
     FLASH_TEXT (rw) : ORIGIN = 0x00000000, LENGTH = 256K /* .text */
-    RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 16K
+    RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 64K
 }
 
 _stack_size = 2K;

src/examples/hello/hello.go

@@ -1,5 +1,7 @@
 package main
 
+import "unicode"
+
 type Thing struct {
 	name string
 }
@@ -46,6 +48,9 @@ func main() {
 	println("Stringer.String():", s.String())
 
 	runFunc(hello, 5) // must be indirect to avoid obvious inlining
+
+	// test library functions
+	println("lower to upper char:", 'h', "->", unicode.ToUpper('h'))
 }
 
 func runFunc(f func(int), arg int) {