Implement "predict" for binr

[smsaladi]

I found your package and functionality quite useful. It would be much easier to use if there were an associated predict method. This would allow calculating cut points on some dataset and then applying these cuts/featurization to new data.

I went ahead and implemented this. In the process, I needed to create some S3 methods.

Because of a change in roxygen2 behavior, I had to make other changes to the documentation code. I tried to commit in logical way to separate this. Also, there were some end of line spaces. Rstudio and atom both clear these, so I committed this separately as well.

Let me know what you think.

> bindata <- bins(iris[,1:4], 5, 5)
> predict(bindata, iris[,1:4]) %>% head
  Sepal.Length Sepal.Width Petal.Length Petal.Width
1            2           3            1           1
2            1           2            1           1
3            1           2            1           1
4            1           2            1           1
5            1           3            1           1
6            2           3            2           2
> 
> withNA <- iris[,1:4]
> withNA[2,1] <- NA
> head(withNA)
  Sepal.Length Sepal.Width Petal.Length Petal.Width
1          5.1         3.5          1.4         0.2
2           NA         3.0          1.4         0.2
3          4.7         3.2          1.3         0.2
4          4.6         3.1          1.5         0.2
5          5.0         3.6          1.4         0.2
6          5.4         3.9          1.7         0.4
> 
> predict(bindata, withNA, labels = TRUE) %>% head
  Sepal.Length Sepal.Width Petal.Length  Petal.Width
1  (5.05,5.65] (3.25, Inf]  (-Inf,1.55] (-Inf,0.249]
2         [NA] (2.95,3.25]  (-Inf,1.55] (-Inf,0.249]
3  (-Inf,5.05] (2.95,3.25]  (-Inf,1.55] (-Inf,0.249]
4  (-Inf,5.05] (2.95,3.25]  (-Inf,1.55] (-Inf,0.249]
5  (-Inf,5.05] (3.25, Inf]  (-Inf,1.55] (-Inf,0.249]
6  (5.05,5.65] (3.25, Inf]  (1.55,4.35] (0.249,1.25]
> 
> predict(bindata, withNA) %>% head
  Sepal.Length Sepal.Width Petal.Length Petal.Width
1            2           3            1           1
2            6           2            1           1
3            1           2            1           1
4            1           2            1           1
5            1           3            1           1
6            2           3            2           2

[sizrailev]

Hi @smsaladi, thanks very much for contributing and for being so thoughtful about separate commits! Your PR is now merged and I will find time to push it to CRAN in the next few weeks.