Changes to work with ASM 5 and Java 8

First change specifies the ASM api version when creating nodes as the default constructor cannot be used with ASM 5 (it checks for subclasses and throws IllegalStateException.) This is compatible with both ASM 4 and 5 on Java 1.7.

Second change actually changes the dependency to ASM 5.0.3 for Java 1.8. There are deprecation warnings but "sbt test" passed on both Java 1.7_60 and Java 1.8_05.