Migrate from joda-time to java 8 time API

[xp-vit]

I believe that the library can be migrated to Java 8 time and dependency on joda-time can be dropped. Please let me know if you agree and I will prepare PR.

thanks

[chriskilding]

Relevant PR for this: #355

[chriskilding]

But unfortunately the maintainers haven't been able to review it yet :/ Which is a problem because there are a couple of subtle differences between Joda and Java 8 Time where the PR needs design guidance - whether to accept the new behaviour and drop the old, or whether to try and emulate the old behaviour of Joda.