v0.3.0

Added

• Add ChildWindow::movable
• ImString now implements fmt::Write

Changed

• Upgrade to cimgui / imgui 1.75
• Bump minimum Rust version to 1.38 (at least backtrace crate requires it)
• Upgrade to glium 0.26 / winit 0.21
• Switch imgui-winit-support to 0.20+ by default. Winit 0.19 support is still
  available via the winit-19 feature flag
• Resources used by examples are no longer included in the published crate

Removed

• Various things that were deprecated in imgui-rs 0.2.0

Fixed

• Fix toggling behavior on using MenuItem::build_with_ref and
  Selectable::build_with_ref.
• ImString nul terminator handling