Support varargs in compressType

First, I want to thank you very much for this powerfull and yet minimalistic API for Java code generation.
I just discovered it last week and fell in love with it. I am going to migrate the [PojoBuilder](https://github.com/mkarneim/pojobuilder) from StringTemplates to JavaWriter.

However, I realized that vararg parameters won't be compressed.
And since I have learned (from reading some of the issues here), that you like community contributions rather than fixing the issues yourself I just added the varargs support myself.

Please don't hesitate to drop that pull request if it is bad in any way.
How about:
```java
boolean isVarargs = type.endsWith(ELLIPSIS);
if (isVarargs) {
  type = type.substring(0, type.length() - ELLIPSIS.length());
}
```