Release 0.16.0

Released 2023-01-22.

• Removed backwards compatible aliases for template functions.
  In ructe 0.7.2 and earlier, a template file page.rs.html resulted in a rust function templates::page(...).
  In 0.7.2, that was changed to templates::page_html(...) and the old name was kept as a deprecated alias.
  However, since the template functions are usually defined within the same crate that defines them, the deprecation warning has usually not been shown, and this removal may still be a surprise to some users (it was even used in examples up to this change).
• Allow more lifetime arguments to templates in template arguments (PR #122, fixes #121). Thanks to @wezm!
• Added axum example (PR #118). Thanks to @vbrandl!
• Updated rsass to 0.27.0 and base64 to 0.21.0.
• Updated dependencies in examples: actix-web 4.2.1, axum 0.6.2, env_logger 0.10.0,
• Dropped support for rust edition 2015 in crates that directly uses ructe.