[R] change internal calls to use keyword args

[jameslamb]

This PR addresses #244

Please do not review until we've merged #266 . I branched off of that PR to avoid dealing with merge conflicts. If/when we merge that, I'll rebase this PR and the diff will make more sense.

[StrikerRUS]

@jameslamb Thank you very much!

Unfortunately, Travis is unhappy. Can you please take a look?

[jameslamb]

yep! The fact that it passed on appveyor tells me it's probably just one of those transient travis things. I'll check.

[jameslamb]

Ha I was too quick to blame Travis. Totally my fault! The package uses occurences (one r) but I accidentally used occurrences (2 r's) in one place. Should be fixed as of my most recent commit

[StrikerRUS]

We haven't configured Appveyor for checking R-package yet :-(

Seems to be another one typo:
'tree_grain_ratio' -> 'tree_gain_ratio' (grain -> gain)

[jameslamb]

whoops! Fixed. I also created #268 so anyone coming to the repo knows appveyor setup is a contribution that would be welcomed.

[jameslamb]

Rebasing right now, now that we've merged #266

[jameslamb]

ok @StrikerRUS @mlampros this is ready for review!

[StrikerRUS]

LGTM!
Please document this in NEWS file.

[jameslamb]

Oh sure, no prob. Just updated the NEWS.md

[mlampros]

thanks