Handle cases where key or payload are subtypes of Integer

[bluesmoon]

Integer values cannot be converted directly to Vector{UInt8}; it requires reinterpret and hton. This MR handles that.

We have separate methods for key and payload so that it can handle all three cases where either one of key or payload are Integers, or both are Integers.

[dfdx]

or both are Integers.

Wouldn't this case lead to ambiguity?

julia> foo(x::Integer, y) = "x is int"
foo (generic function with 1 method)

julia> foo(x, y::Integer) = "y is int"
foo (generic function with 2 methods)

julia> foo(x, y) = "x and y are Any"
foo (generic function with 3 methods)

julia> foo(1, 1)
ERROR: MethodError: foo(::Int64, ::Int64) is ambiguous.

Candidates:
  foo(x::Integer, y)
    @ Main REPL[1]:1
  foo(x, y::Integer)
    @ Main REPL[2]:1

Possible fix, define
  foo(::Integer, ::Integer)

Stacktrace:
 [1] top-level scope
   @ REPL[4]:1

[bluesmoon]

@dfdx hopefully these updates handle all cases as well as the consumer side.

[dfdx]

Looks great, thank you!