Enable Java 8 build (with a Java8 profile)

Enable Java 8 build in travis (in addition to Java7)

There's a findbugs incompatibility, so I've introduced a profile which disables it under Java8.

The profile also disables strict javadoc html checking
Support bring-your-own `MetricsRegistry` in `Bootstrap`.
Updating healthcheck example output

This now outputs in JSON instead of plain text.
Updated README to reflect version in pom.xml
Merge branch 'master' of github.com:dropwizard/dropwizard
Add Jochen Schalanda to developers in parent POM
Merge pull request #566 from reines/documentation_updates

Update example healthcheck output in the documentation
Merge pull request #568 from joschi/update-contributors

Add Jochen Schalanda to developers in parent POM
Use textual timezone designations for committers
Refactor Duration

- Initialize suffixes at one shot
- Delegate whitespace handling to the regex
- Remove redundant checking on time unit type from the regex
- Derive count and unit from the regex matching result
Refactor Size

- Initialize suffixes at one shot
- Delegate whitespace handling to the regex
- Remove redundant checking on size unit type from the regex
- Derive count and unit from the regex matching result
Merge pull request #569 from arteam/refactor_utils

Refactor Duration and Size a bit
Allow discarding any cached principal for a collection of credentials
satisfying a given predicate.
Merge pull request #570 from florinn/invalidateCredentialsByPredicate

Invalidate credentials by Predicate
Fix regression of metrics not reporting over JMX

Thanks @gtrog for spotting this one!

Closes #552.
Merge pull request #548 from gdusbabek/bootstrap_use_getter_for_metrics_registry

Support bring-your-own MetricsRegistry in Bootstrap.
Merge pull request #556 from betrcode/patch-1

Updated README to reflect version in pom.xml
Merge pull request #498 from davidillsley/java8

Enable Java 8 build in Travis CI
Merge branch 'master' of https://github.com/dropwizard/dropwizard