0.16.0

Full Changelog

• BREAKING! #126 Improve compile times
  • Inclusion of <functional> and <iterator> hurts compilation times, so
    their usage is removed for core headers (all, but adaptor).
  • allow only functors in var_signal::modify() (any invokable were valid
    before). It allows not including <functional> in <ureact/signal.hpp>
• #134 Get rid of issue_template.md
• #136 Work around broken ureact::merge with latest MSVC in c++20 mode
• #133 Fix MSVC's /W4 warnings