CLI cannot accept a path input, though its help and the compiler both support one #501

The CLI help advertises a path input:

usage: elixirscript <module | path> [options]
<path> the path to .ex(s) files to compile

ElixirScript.Compiler.compile/2 does support it — def compile(path, opts) when is_binary(path) plus the Path.wildcard/1 handling was added by #420 — but the CLI never passes a path through, because handle_input/1 maps every argument token through Module.concat/1:

defp handle_input(input) do
  input
  |> Enum.map(fn x -> String.split(x, [" ", ","], trim: true) end)
  |> List.flatten()
  |> Enum.map(fn x -> Module.concat([x]) end)
end

(lib/elixir_script/cli.ex:91-96)

So a path becomes an atom, the when is_binary(path) clause is unreachable from the CLI, and the compile aborts:

$ mix run -e 'ElixirScript.CLI.process({["test/fixtures/list_ops.ex"], []})'
[warn] ElixirScript: :"Elixir.test/fixtures/list_ops.ex" is missing or unavailable
** (MatchError) no match of right hand side value: nil
    lib/elixir_script/passes/find_used_functions.ex:36: ElixirScript.FindUsedFunctions.walk_module/2

Passing the same path straight to the compiler works, so only the CLI wiring is missing.

Reproduced on cc8a08a with Elixir 1.11.4 / OTP 23.

Filed as an issue rather than a PR because a fix needs a disambiguation rule: a bare token can be either a module name or a relative path (Atom vs ./Atom, my/path vs My.Path), so "treat it as a path when it names an existing file or directory" is a behaviour change worth agreeing on first.