Allows codec to work with auto-value types

[codefromthecrypt]

Auto-Value writes immutable value types based on a user defined abstract class. It also supports generating factories, based on a user-defined interface. The following change adjusts swift codec to work both reflectively and via ASM.

Here's an example type that works following this change:

@AutoValue
@ThriftStruct(value = "LogEntry", builder = AutoValue_LogEntry.Builder.class)
public abstract class LogEntry {

  public static Builder builder() {
    return new AutoValue_LogEntry.Builder();
  }

  @ThriftField(value = 1)
  public abstract String category();

  @ThriftField(value = 2)
  public abstract String message();

  @AutoValue.Builder
  public interface Builder {

    @ThriftField(value = 1)
    Builder category(String category);

    @ThriftField(value = 2)
    Builder message(String message);

    @ThriftConstructor
    LogEntry build();
  }
}

The notable change for ASM is that generated codecs are now placed in the same package as the value type, and defined in the same classloader. Also, this makes sure we use the correct injection method (ex. from the implementing class as opposed to the interface).

Tests pass and I've also verified with zipkin.

Closes #273

[codefromthecrypt]

fyi @kristofa @spencergibb @eamonnmcmanus

[codefromthecrypt]

weird.. all the comments got stripped.. anyway @andrewcox lemme know if you've anything needed before merge.

[codefromthecrypt]

any timeframe on this? I'd love to take out my build hack https://github.com/openzipkin/zipkin-java/blob/master/swift-codec/pom.xml

[codefromthecrypt]

hate to nag, but is this project on pause?