readHDFStextFile: Experimental HDFS text reader helper function
In datadr: Divide and Recombine for Large, Complex Data

Experimental helper function for reading text data on HDFS into a HDFS connection

1 2	readHDFStextFile(input, output = NULL, overwrite = FALSE, fn = NULL, keyFn = NULL, linesPerBlock = 10000, control = NULL, update = FALSE)

`input`	a ddo / ddf connection to a text input directory on HDFS, created with `hdfsConn` - ensure the text files are within a directory and that type = "text" is specified
`output`	an output connection such as those created with `localDiskConn`, and `hdfsConn`
`overwrite`	logical; should existing output location be overwritten? (also can specify `overwrite = "backup"` to move the existing output to _bak)
`fn`	function to be applied to each chunk of lines (input to function is a vector of strings)
`keyFn`	optional function to determine the value of the key for each block
`linesPerBlock`	how many lines at a time to read
`control`	parameters specifying how the backend should handle things (most-likely parameters to `rhwatch` in RHIPE) - see `rhipeControl` and `localDiskControl`
`update`	should a MapReduce job be run to obtain additional attributes for the result data prior to returning?

## Not run: 
res <- readHDFStextFile(
  input = Rhipe::rhfmt("/path/to/input/text", type = "text"),
  output = hdfsConn("/path/to/output"),
  fn = function(x) {
    read.csv(textConnection(paste(x, collapse = "\n")), header = FALSE)
  }
)

## End(Not run)