use * for pointer type instead of &

See #770

To help automatically translate code, see the
zig-fmt-pointer-reform-2 branch.

This will convert all & into *. Due to the syntax
ambiguity (which is why we are making this change),
even address-of & will turn into *, so you'll have
to manually fix thes instances. You will be guaranteed
to get compile errors for them - expected 'type', found 'foo'

test/gen_h.zig

@@ -1,6 +1,6 @@
 const tests = @import("tests.zig");
 
-pub fn addCases(cases: &tests.GenHContext) void {
+pub fn addCases(cases: *tests.GenHContext) void {
     cases.add("declare enum",
         \\const Foo = extern enum { A, B, C };
         \\export fn entry(foo: Foo) void { }