All bin dirs already on path for lifecycle scripts

NPM puts all node_module bin directories on the path before running lifecycle scripts.  So package bin files can be executed as if they are installed globally.
Add rtree to dev dependencies to let others run the perf script

Adding `rtree` to dev dependencies and adding `perf` to the npm scripts lets developers run performance benchmarks without having to install `rtree` globally.  Non-lifecycle scripts can be run with `npm run`.  E.g.

    npm run perf
Merge pull request #13 from tschaub/dev-setup

Basic instructions on running tests and performance benchmarks