Add erserve:controlling_process/2 to hand over control of a connectio…

…n to a new process

Improve handling of large Erlang integers: they will be transported a…

…s int, double or string depending on size.

Improve handling of NaN/NA/Inf/-Inf in doubles

Add support for NaN/Inf/-Inf in doubles; add more helpers to translat…

…e between R and Erlang representations of data

Correctly handle empty arrays of strings

Add some info about NAs to readme

Add support for uploading NA values in ints and doubles.

It also works for booleans, if you both write and read them via Rserve/erserve,
but if you for instance upload a boolean array with NAs in it and then save()
it, and load() it up in a regular R instance, that R will see the NAs as TRUE.

Add support for sending boolean arrays to R

Add missing erserve: in front of open/close.

Fix issue with transferring xt_array_str.

Turns out Rserve doesn't want to eat what it serves. It sends xt_array_str with \0-terminated strings padded out with
\1 to take a multiple of 4 bytes. But it only expects the \1-padding at the end of the array and not at each individual
string when it receives data.