Human-friendly method symbol format

Before:
```
targetClassName=com.google.common.base.Verify, methodName=verify, interfaceMethod=false, descriptor=(ZLjava/lang/String;Ljava/lang/Object;)V
```

Better:
```
void com.google.common.base.Verify.verify(boolean, java.lang.String, java.lang.Object)
```

(feedback from Garrett)

Created branch "human_friendly_signature" but I may change the structure of JarLinkageError to hold LinkageErrorCause class.