Boot sha2-asm

Stick with pure Rust until someone can write a benchmark that
demonstrates that sha2-asm adds value. If we go with a GPU
implementation first, we may never need to do that.

.travis.yml

@@ -9,7 +9,7 @@ matrix:
   - rust: stable
   - rust: nightly
     env:
-    - FEATURES='asm,unstable'
+    - FEATURES='unstable'
 before_script: |
   export PATH="$PATH:$HOME/.cargo/bin"
   rustup component add rustfmt-preview

Cargo.toml

@@ -41,12 +41,10 @@ codecov = { repository = "loomprotocol/silk", branch = "master", service = "gith
 [features]
 unstable = []
 ipv6 = []
-asm = ["sha2-asm"]
 
 [dependencies]
 rayon = "1.0.0"
 sha2 = "0.7.0"
-sha2-asm = {version="0.3", optional=true}
 generic-array = { version = "0.9.0", default-features = false, features = ["serde"] }
 serde = "1.0.27"
 serde_derive = "1.0.27"

README.md

@@ -128,5 +128,5 @@ $ rustup install nightly
 Run the benchmarks:
 
 ```bash
-$ cargo +nightly bench --features="asm,unstable"
+$ cargo +nightly bench --features="unstable"
 ```