option to save as ASCII instead of binary

Hi Gergely,

The idea of this package is nice, but binary objects can be tricky.
How about introducing an option somewhere to save variables in plain ASCII files instead of binary.

Something in the line of:
save(x, ascii = TRUE, file = "x.xz", compress = "xz")

You get compression and the final result is the same (having one tar file containing all of these variables as separate files to be read). Probably less fast in the performance benchmark, but gaining complete portability over time.