refactor; add bin.

tests/sha256.rs

@@ -1,5 +1,4 @@
-mod common;
-use common::hexstr;
+use emsha::hexstr::to_hex;
 use emsha::sha256;
 use emsha::{Hash, Result};
 
@@ -65,7 +64,7 @@ fn test_golden_tests() -> Result<()> {
     while i < golden_tests.len() {
         h.update(golden_tests[i].input)?;
         h.finalize(&mut d)?;
-        hexstr(&d, &mut s);
+        to_hex(&d, &mut s);
         assert_eq!(s, golden_tests[i].output);
         h.reset()?;