Investigate if test coverage can be improved

[shamblett]

Recent updats to the package, see #85 hav eresulted in a decreas ein code coverage. This should be investigated and corrected where necessary.

[shamblett]

Maybe an opportunity to have a look at this package on this issue.

[shamblett]

The prettyprinter code had no unit tests at all, test suite added, also a bug concerning nested maps in the pretty printer was fixed.

Typed data tests added to increase coverage in this area.

Overall coverage now at 79.6% an improvement but more can be done.

[shamblett]

Added more unit tests in for value types, coverage is now at 88.1%. I believe this is now sufficient.

As for mutation testing I'm not convinced now this package will benefit any from this. There are 500+ unit tests, most of which are testing against values specified in RFC's, I believe this is sufficient for this package.

Package re published at version 6.5.1.