std::time replacement for wasm

[iceiix]

The wasm32-unknown-unknown target does not support std::time, will need to find a replacement for 🕸️ Web support #446

[iceiix]

Uses of std::time:

• src/main.rs - Duration, Instant - FPS cap (optional)
• src/entity/player.rs - Instant - when_last_jump_pressed/released
• src/screen/server_list.rs - Duration - ping
• src/ui/logo.rs - SystemTime, UNIX_EPOCH - animation
• src/world/mod.rs - Instant - lighting update ticks
• protocol/src/protocol/mod.rs - Duration, Instant - server ping

https://doc.rust-lang.org/std/time/struct.Instant.html - opaque nondecreasing clock, only useful with Duration
https://doc.rust-lang.org/std/time/struct.Duration.html - seconds and nanoseconds (if not precise, rounded up)

The web platform has performance.now(), returning milliseconds increasing at a constant rate, not limited to ms-precision (floating-point allows up to µs precision, but Firefox at least rounds to 1 ms). Sounds exactly like what we want for Instant and Duration.

Found this crate, a drop-in replacement (would be nice if these crates could override std, alas...) for std::time::Instant working on WASM too: https://lib.rs/crates/instant https://github.com/sebcrozet/instant

There's also https://lib.rs/crates/wasm-timer for std::time::Instant and futures-timer (tokio-timer on native). https://lib.rs/search?q=wasm+std This looks promising too: https://lib.rs/crates/wasm_thread "An std thread replacement for wasm32 target"