Release 0.2.0

This release is primarily aimed at ensuring generated code passes lints.

Breaking changes

• Renamed TreeMatcher::set_input_type() to TreeMatcher::input_type().

Changes

• Made sure generated functions pass Clippy’s pedantic lint group:
  • Changed to add #[must_use] to generated functions by default.
  • Added trivial documentation about what errors are returned by a few
    functions.
  • Disabled clippy::single_match_else lint within generated match
    functions, since we sometimes generate match statements with a single arm.
  • Disabled clippy::too_many_lines lint within generated match
    functions, since such functions can be extremely long.
• Added support for setting documentation on generated functions. This also adds
  docs to the stub function used in disabled Clippy mode which allows it to be
  used with #![warn(missing_docs)].