Add xxd -i (and xxd -ri).

Add xxd -i (and xxd -ri).

The original xxd doesn't support -r with -i. The original also outputs
"unsigned char name[] = { ... };" for input other than stdin, but that
actually makes it less useful --- many languages support array
initializers, but far fewer support that exact declaration syntax.

Also fix the -c range checking and defaulting: ><= in the argument string
only works for floating point arguments.

Bug: http://b/64711851