Add simple configuration file for AppVeyor.
Add simple configuration file for AppVeyor.

There is just one build job for now.

songy23/instrumentation-java,bogdandrutu/opencensus-java,songy23/instrumentation-java,bogdandrutu/instrumentation-java,bogdandrutu/instrumentation-java,sebright/opencensus-java,sebright/opencensus-java,census-instrumentation/opencensus-java,dinooliva/instrumentation-java,census-instrumentation/opencensus-java,dinooliva/instrumentation-java,sebright/opencensus-java,bogdandrutu/opencensus-java,bogdandrutu/opencensus-java,census-instrumentation/opencensus-java,sebright/instrumentation-java,ubschmidt2/instrumentation-java,songy23/instrumentation-java,sebright/instrumentation-java,ubschmidt2/instrumentation-java