Add corrosion as a subdirectory, CMake fixes

Store all snowflakes in a separate array, achieving performance increase of about 10% for the whole engine on winter maps

Avoid creating unused string that is quite costly to produce

Improve pas2c rtl performance by avoiding double iteration on strings

Implement triggering advancement of simulation in qmlfrontend

Implement key bindings

Handle game view resize

Improve AI aiming with minigun

Wonder if anyone is trying to build this game anymore

Allow to move camera by dragging mouse cursor over game field

Fix build

Port QML frontend to Qt6, use rendering to framebuffer object

Start on adopting corrosion

Merge default

Fix type