Remove Builder() for Kotlin support

[matthiasrupp]

The static method Builder() should be removed

• It violates against the Java naming conventions
• It is more convenient to write new Polygon.Builder() instead of Polygon.Builder()

And most important:

• It makes the library unusable with Kotlin! ( Polygon.Builder() would be an constructor invocation )

[AgustRuiz]

This totally should be applied