Change interface symbol from ~ to &

compiler/test-data/data/simpleinterface/main.fspl

@@ -1,4 +1,4 @@
-Numbered: (~ [number]: Int)
+Numbered: (& [number]:Int)
 Number: Int
 Number.[number]: Int = [.this]
 

compiler/test-data/usr/src/fspl/io/io.fspl

@@ -1,7 +1,7 @@
 + [print   string:String]: Index = cstdio::[write 1 [~*Byte string] [#string]]
 + [println string:String]: Index = [+ [print string] cstdio::[write 1 '\n' 1]]
 
-+ Writer: (~ [write buffer:*:Byte]: Index)
++ Writer: (& [write buffer:*:Byte]: Index)
 + File: cstdio::FileDescriptor
 + File.[write buffer:*:Byte]:Index =
 	cstdio::[write