Data repo

[ThierryO]

This PR solves #301. It is mainly a port from functions available in our n2khelper package. Therefor, the testthat framework is used for unit testing.

[coveralls]

Coverage decreased (-1.1%) to 76.507% when pulling 5d72b62 on ThierryO:data_repo into 047a9ba on ropensci:master.

[ThierryO]

Don't merge yet. I'll be adding some more unit tests

[coveralls]

Coverage increased (+0.2%) to 77.852% when pulling 1267d58 on ThierryO:data_repo into 047a9ba on ropensci:master.

[coveralls]

Coverage increased (+0.3%) to 77.941% when pulling 36e3d63 on ThierryO:data_repo into 047a9ba on ropensci:master.

[coveralls]

Coverage increased (+0.3%) to 77.941% when pulling 36e3d63 on ThierryO:data_repo into 047a9ba on ropensci:master.

[coveralls]

Coverage increased (+0.3%) to 77.87% when pulling 3a44df0 on ThierryO:data_repo into 047a9ba on ropensci:master.

[stewid]

Hi @ThierryO

I have looked through the code and have identified two calls to command-line git that we must replace with functionality in git2r. Unfortunately, neither git ls-tree -r HEAD path nor git log -n 1 --date=iso path are yet supported in git2r, but I can fix that, hopefully tomorrow. I have also identified a couple of places where we can use functionality already in git2r, for example, is.git -> in_repository. But let me start by adding new functionality.

Thanks

[ThierryO]

I'll update the PR when the new functionality becomes available.

[stewid]

I have added the ls_tree functionality.

head(ls_tree(repo = "."))
#>     mode type                                      sha path            name   len
#> 1 100644 blob 1257be2f7b69861fd93ec186b063c05b87f296dc        .Rbuildignore   245
#> 2 100644 blob b61efef40fb2b94bad32c5f15244e7cb8fa3c491           .gitignore   255
#> 3 100644 blob 87a0f9d2621ee32df25023a70c819a6144dc2d3c          .travis.yml   898
#> 4 100644 blob c5cde7bc087d0595661f9ffc8737e5455f79e3b9      CONTRIBUTING.md  7811
#> 5 100644 blob 31857cf173efc03ceda2d65b6d0e301faed7693d          DESCRIPTION  1396
#> 6 100644 blob d7f105139782ab695d86613e343916f7372f4ac0              LICENSE 18026

I'm currently changing S4 methods to standard R functions and S4 classes to S3 classes. This might take me a couple of weeks. Since that work also affect code in this PR, I let you know when I have completed it.

[ThierryO]

I'm curious why you want to switch from S4 to S3.

[stewid]

The reason I want to switch to S3 is to simplify the design and make future development easier. With this change, most of the R functions are one-liners that only pass data to the C-level of git2r.

[ThierryO]

I'm working on a new (and improved) version of this based on the new S3 classes.