Timestamps

[aappling-usgs]

Timestamp checking is working.

Here's my best visual explanation of how vizlab treats file currency and timestamps so far (needs work, but it's a start):

The timestamp functionality is demonstrated in https://github.com/USGS-VIZLAB/vizlab/pull/316/files#diff-3066b18354ab4c8e1b10c0daa72dbcfe

I also updated the vignettes.

[aappling-usgs]

tests work when run at console but fail w ctrl-shift-t. pushing here to see how travis does with it

[coveralls]

Coverage decreased (-11.0%) to 65.119% when pulling 86ac0cb on aappling-usgs:timestamps into 475953d on USGS-VIZLAB:remake.

[coveralls]

Coverage decreased (-11.0%) to 65.119% when pulling cd3484e on aappling-usgs:timestamps into 475953d on USGS-VIZLAB:remake.

[aappling-usgs]

It works! Sorry for the giant PR, but it's what was needed to get timestamps handled and properly tested...OK, and to get the testviz a bit more compliant with the style guide too. For reviewing, it's probably easiest to start with the tests to see how the package is supposed to behave. @ldecicco-USGS , do you have time to review this?

[aappling-usgs]

also, createRemakefiles is atrociously long and i know it. i'm working on a refactor for an upcoming PR

[aappling-usgs]

Here's the cleaned-up version of createRemakefiles: https://github.com/aappling-usgs/vizlab/compare/timestamps...aappling-usgs:parameters?expand=1#diff-3100aa6afab755cba48769133597a7a8. I'm not sure how to create a clean PR for it before this one is merged because it depends on this one, but I'll create it as soon as we're through with this one.

[ldecicco-USGS]

Pulled it down, seemed to work as I expect. Super cool