0.42.0: Export enum (#476)

• Support for Exporting enumerations to Godot, to do this, flag your
  enumerations with CaseIterable, and then use @Export(.enum).
  See the Exports
  Documentation
  for additional information - Miguel.

• Fix compilation when used with codebases that define their own
  Variant type, fix from Stefan Urbanek.

• Fixes Godot documentation conversion by handling url fragments.
  Miguel.

• Fix dynamic type of singletons (Gergely Kis, Gabor Koncz)

• Performance: Exposed withUnsafeConstAccessToData for
  PackedByteArray, which avoids a data copy of the underlying buffer.
  Improvement by Kevin Watters.

• Performance, all accessors to Packed data arrays now avoid copies, improvement by Kevin Watters.

• Handle return as a special keyword, to fix compilation for some
  scenarios, fix by Josh Bromberg.

• Various documentation updates, Miguel, Mikhail Tishin, Dolapo Falola