go/scanner: accept 'i' suffix orthogonally on all numbers

This change accepts the 'i' suffix on binary and octal integer
literals as well as hexadecimal floats. The suffix was already
accepted on decimal integers and floats.

See also the respective language in the spec change:
https://golang.org/cl/161098

Change-Id: I0c182bdf58f8fd1f70090e581b3ccb2f5e2e4e79
Reviewed-on: https://go-review.googlesource.com/c/162880


Reviewed-by: Ian Lance Taylor <iant@golang.org>