Changed some testing outputs from stderr to stdout
Changed Expr::Compare to workaround gcc-4.4 bug
Added optional static bounds for Params.

They're exprs, so you can declare things like one param being less
than another param. If you want to introspect them as constants,
use as_const_int or as_const_float from IROperator.h. For constants that
aren't int32 or float32 you'll need to dig through a cast as well, e.g.:

Expr e = param.get_max_value();
const Internal::Cast *c = e.as<Internal::Cast>()
if (c) return as_const_int(c->value);
else return NULL;