v0.6.0

[v0.6.0] - 2020-04-04

Added

• RectangleByPoints function in Polygon, creates a new Polygon rectangle
  between the two provided points.
• Frustum culling, only rendering what is on screen to improve performance.
• Text rendering with the TextSystem, FontAsset and Text Component.
  • Supports any font loaded through the browser.
  • Specify font size, weight, family, and other tuning options through
    FontAsset for a font.
  • Specify z order, alignment, spacing, color, offset and shaders through
    Text component for a specific piece of text.
  • New fragment shader for rendering text, default_text_fragment.
• Renderable can now have additional information attached to them by
  pre-rendering systems, which can be accessed by shaders.
• Material represents shaders and a texture to apply. Can be applied to
  entities, allowing custom shaders.
• Can now load custom shaders using a ShaderAsset.

Changed

• Merged SpriteSystem and UISystem into a single system - SpriteSystem.
• Rectangle function in Polygon renamed RectangleByDimensions.
• RectangleByDimensions takes an optional origin point, default 0,0.
• All sprites require a Texture now, no longer optional.
• ImageSystem renamed to HTTPImageSystem.
• Group by texture for WebGL rendering to reduce texture switching and improve
  performance.

Fixed

• Polygon.PointInside does not mistakenly predict point to the right of the
  polygon are inside.