Change all Array and Vector to AbstractArray and AbstractVector

[biogeo]

Changing all Array and Vector type specifications in method signatures to AbstractArray and AbstractVector to make code more generic, as per #86.

[mlubin]

Could you add some tests of this functionality?

[biogeo]

Sure, I'm not sure exactly what to test though. Is it reasonable to add a dependency on, e.g., DataFrames for the purposes of testing with a DataArray?

[mlubin]

You could add a testing dependency on DataFrames (i.e., in test/REQUIRE). You could also just test with subarrays.

[biogeo]

Sounds good, will do when I have a chance.

[biogeo]

I added tests, essentially by replicating existing tests using SubArrays instead of Arrays.

[biogeo]

Travis tests for Julia nightly release seem to be failing, but not on a line that makes sense to me based on anything I changed.

[biogeo]

I can confirm that I get the same test failure when running Pkg.test on Julia 0.5.0-dev+2440 (the current dev version on JuliaBox) on the current master branch, so I don't think the failed test is anything to do with this PR.

[pkofod]

I guess this requires changing sub to view? Or include some mechanism for supporting both v0.4 and v0.5 ?