Allow depending on mruby build, support passing args to rake

[jethrodaniel]

Changes

• update addMruby to return a build step users can use to ensure rake has already been ran
  • update example to include embedding bytecode produced by mrbc using @embedFile
  • Also supports passing in arguments to rake directly
  • NOTE: this PR targets https://github.com/dantecatalfamo/mruby-zig/pull/4, which in turn targets https://github.com/dantecatalfamo/mruby-zig/pull/3