0.13.0

• Update Duktape to version 2.2.0, rebuilding all necessary
  configuration and header files.
• [upstream change]
  LibDUK::Compile::* and LibDUK::BufObj::* constant values have
  been changed - remap these constants to their updated values.
• [upstream change]
  LibDUK::Bool is now of type UInt32 (as opposed to Int32).
• Add bindings for new public API methods:
  duk_push_proxy, duk_seal, duk_freeze, duk_require_object, duk_is_constructable
  and duk_opt_xxx methods. The duk_opt methods work similar to
  duk_require_xxx, but allow a default value to be passed in that
  is used when there is no value at the given stack index.
• Alias LibDUK::Number as Float64 for more simple type changes in
  the future.
• Add the Duktape::API::Opt module to encapsulate binding wrapper code
  for the duk_opt methods implemented.
• Run all code through the crystal 0.24.1 formatter.
• See duktape releases for more info.