preparing logging for configuration and more... (rework #1)

hi. thanks very much for bringing this to ground. i'd like to suggest two changes to make this module a little easier to integrate.

first, instead of using console.log(), the caller really ought to be able to provide a logging function - this pull request does about half that: it defines the default logging (which does use console.log) and allows the caller to define nest.logger to call their own logging routines.

second, i'd normally expect to see callbacks always have two parameters, viz., (err, result). although this is true for nest.login, it's not true for most of the other functions. before i submit another pull request, i wanted to get your thoughts on that.

thanks for the excellent package!

best,

/mtr