Cleanup with an emphasis on checkstyle.


Build changes:
 * Made the build task the default from the main directory.
 * Minor formatting changes for clarity.
 * Made findbugs work only on the main source set for the moment.
 * Enabled showWarnings for checkstyle for metrics3 so that people won't ignore it.
    
Checkstyle-related changes:
 * Made the project conform to the checkstyle format defined.
 * Modified the defined format to add warning suppression with comments.
 * Modified the defined format to remove the FinalClass check, since
    it wasn't relevant for this project.

Other changes:
 * Project was double-reporting all IOExceptions at different warning levels. This has been corrected.
 * Silenced warnings when gauges aren't numbers. This fits with the standard by the Graphite reporter.
 * Added supported for BigInteger and BigDecimal.
 * Made the tests more permissive (they were testing that p95 was reported before p99, and really statsd
    doesn't care at that level of detail). Now they are less implementation-specific.
 * Named the logger consistently between files.
 * Added a basic set of JSR305 annotations.
 * Made the formatting consistent between metrics2-statsd and metrics3-statsd.