Changed all requires to relative paths

when using nvm (which is the only practical way of having multiple installations of node and the easiest way to update node), sibilant doesn't work because it uses code like `require("sibilant/` this breaks down with nvm because nvm puts node modules in a different path than the regular npm install directory. All I did was change these paths to relative paths in the `src/`, `test/` and `lib/` directories. These relative paths will work no matter what to npm setup is.