Add tests

[ghost]

I added bunch of regression tests. There are a few that aren't currently passing, I left them commented out so the tests would succeed overall. (I couldn't find a "TODO" test mechanism in testthat so I opened a feature request for it.)

[ghost]

I also have a "FixBugs" branch that picks up where this one leaves off, fixing the problems I found in the tests:

kenahoo/pack@AddTests...kenahoo-windlogics:FixBugs

If you approve this PR I can rebase my FixBugs branch on top of it for a cleaner merge.

[joshuaulrich]

Thanks! How did you create the raw vectors you're testing against?

Regarding your "FixBugs" branch: can you please provide more details in the commit message about what is being fixed? I try to follow these suggestions, paying special attention to explaining the problem and the solution.

[kenahoo]

To find the appropriate raw vectors, sometimes I used Perl (in those cases I pasted the Perl code as comments into the tests), sometimes just mental conversion between decimal & hex, I guess. I can try to make them more explicit.

[joshuaulrich]

This has been merged into the develop branch. Note that I made a few changes and squashed all the commits into a single commit.

[ghost]

Good point about the native format. Looks like we can check .Platform$endian to be aware of the machine type.