Current issues blocking the webasm build

[InnocentusLime]

These issues are blocking the release of the current version of gluttony for webasm:

• bevy_framepace doesn't work in webasm #1 (isn't really blocking the build itself)
• The fix of Strange behaviour coming from the asset loader #9 is Desktop-only
• Async save loading can't be implemented the same way as it was implemented for Desktop (async save loading is temporarily removed)
• Tiled map loader limitation  #47
• The env for the WASM version is not ready
• tiled crate uses zstd, which doesn't seem to compile for wasm

[InnocentusLime]

Adding to the 1.0 milestone, since it was determined that the webassembly build is important for the project.

[InnocentusLime]

Async save loading can be implemented using async_channels, freeing the engine from the need to poll tasks directly.