Rename from string to from slice and fuck utf8

src/machine.rs

@@ -76,8 +76,8 @@ impl Machine {
         Machine::new_from_reader(reader)
     }
 
-    pub fn new_from_string(source: String) -> Result<Machine> {
-        let reader = IJVMReader::new_from_string(source);
+    pub fn new_from_slice(source: &[u8]) -> Result<Machine> {
+        let reader = IJVMReader::new_from_slice(source);
         Machine::new_from_reader(reader)
     }