Updated version number to reflect hadley's advice

http://r-pkgs.had.co.nz/description.html#version
http://r-pkgs.had.co.nz/release.html

The first release on CRAN will be 1.0.0.  We'll increment to 1.0.1, 1.0.2 as we fix bugs, etc., and bump to 1.1.0 when we release the next batch of major features (multi-class optimization, early stoping in greedy optimization if the error decreases.).