Use bindings package when requiring node bindingins. Fixes #242

[nvartolomei]

node-gyp uses node build configuration when building addons.

Because lwip was looking only in build/Release folder it wasn't working when installed on a debug build of node.

node-bindings solves this issue, it will look in all possible places where the bindings can be.

[EyalAr]

Cool, thanks @nvartolomei