Release new version

Features:
    - Particle systems can now specify a maximum dt per step
    - Animation key-framing & timing system now supports objects with simulation
    - Mixture/multiple importance sampling for correct low-variance direct lighting
        - New BSDF, point light, and environment light APIs that separate sampling, evaluation, and pdf
        - Area light sampling infrastructure
        - Removed rectangle area lights; all area lights are now emissive meshes
        - Reworked PathTracer tasks 4-6, adjusted/improved instructions for the other tasks

Bug fixes:
    - Use full rgb/srgb conversion equation instead of approximation
    - Material albedo now specified in srgb (matching the displayed color)
    - ImGui input fields becoming inactive no longer apply to a newly selected object
    - Rendering animations with path tracing correctly steps simulations each frame
    - Rasterization based renderer no longer inherits projection matrix from window
    - Scene file format no longe...