ImGui-SFML 2.6 release notes

[oprypin]

Draft of release notes:

Support the full key range from imgui v1.87, e.g. ImGui::IsKeyDown(ImGuiKey_Q) now works (#197)
Expanded API: Propagate boolean error state from Texture.create to methods such as Init (#191)
Expanded API: Make all joystick axes and thresholds configurable, not just the left stick (#197)
API change: Fix typo in method names: "joytick" -> "joystick" (#201)

Propagate window resize events to imgui (#222)
Fix dimming of imgui modal dialogs (004efd8)
Fix the window resize cursor not being shown on Windows (#193)
Fix memory leak from cursors (#194)

Fix for changes in imgui around ImGuiKey (#219)
Fix deprecations from SFML 2.5/2.6 (#187, #205)
Fix for changes in upcoming SFML 3 (#205, #208, #217, #232, #250)
Fix various compiler warnings (#235, #245, #246)

Raise C++ standard to C++11 (#203)
Raise CMake requirement from 3.1 to 3.10 (#244)