add wasm-resolver which uses rust-crypto-wasm

Fixes #33
this enables building for wasm with

    cargo build --no-default-features --features=wasm-resolver

Cargo.toml

@@ -15,6 +15,7 @@ keywords = ["noise", "protocol", "crypto"]
 default = ["default-resolver"]
 nightly = ["blake2-rfc/simd_opt", "chacha20-poly1305-aead/simd_opt", "x25519-dalek/nightly"]
 default-resolver = ["chacha20-poly1305-aead", "blake2-rfc", "rust-crypto", "x25519-dalek", "rand"]
+wasm-resolver = ["chacha20-poly1305-aead", "blake2-rfc", "rust-crypto-wasm", "x25519-dalek", "rand"]
 hacl-star-resolver = ["hacl-star"]
 hacl-star-accelerated = ["hacl-star-resolver", "default-resolver"]
 ring-resolver = ["ring"]
@@ -40,8 +41,9 @@ static_slice = "0.0.3"
 chacha20-poly1305-aead = { version = "^0.1", optional = true }
 blake2-rfc = { version = "^0.2", optional = true }
 rust-crypto = { version = "^0.2", optional = true }
+rust-crypto-wasm = { version = "^0.3.1", optional = true }
 hacl-star = { version = "=0.0.11", optional = true }
-rand = { version = "^0.5", optional = true }
+rand = { version = "^0.5", optional = true, features = ["stdweb"] }
 ring = { version = "^0.13.0", optional = true }
 x25519-dalek = { version = "^0.3", optional = true, default-features = false, features = ["std", "u64_backend"] }