Added link to project website
don't export gwsm.estimator for now
added example for get.fn
devtools-generated changes to docs
changed error msg if missing != 'ignore'
minor spacing changes
added @example to docs for nsum.estimator
changed weights in example.survey

these used to be relative weights, which could be confusing to
users because then weighted totals don't look very different from
unweighted totals. i've converted them to be absolute weights, based
on an assumed population size of 10e6.
auto-generated changes to docs