add further documentation

[AdamSpannbauer]

adds roxygen2 style documentation for package to address #43

[eddelbuettel]

That looks straightforward enough.

As a general viewpoint, I do not believe in replacing working setups just for the sake of making changes. So I would delete lines 1 to 24 of annoy.R -- the per-package Rd file is perfectly content to have been hand-written. Plastering over it also, among other things, destroys commit history for that file.

[AdamSpannbauer]

Seems reasonable to me. I deleted the roxygen2 style RcppAnnoy-package docs and removed the alias lines for the AnnoyIndex items that were in RcppAnnoy-package.Rd.

[eddelbuettel]

Sorry for the delay, I am usually quicker. I am also working on some updates to testing as a first test of the new tinytest by @markvanderloo and both of those changes should go out relatively "soon".