0.4.0

Changed:

• moved implementations of XML-RPC clients, servers, and the axum server support into separate
  crates, available as optional features of the top-level dxr crate
• moved to more powerful cargo feature syntax for optional and conditional dependencies
• server: refactored method call Handler trait to allow the handler function to be async

Fixed:

• methodResponse must apparently always contain exactly one value
• methodParameters contain an array of parameters that contain values, not a parameter that
  is an array of values

Both these fixes required minor changes to the public API, which is why they cannot be backported
to the 0.3.x branch.

Added:

• implemented of FromDXR for fixed-size arrays
• implemented support for struct fields that are fixed-size arrays in the derive macros

Updated dependencies:

• updated axum version from 0.4 to 0.5
• updated quick_xml version from 0.22 to 0.23