Completed integration of node-pre-gyp into Node library

binding.gyp

package.json

src/node/index.js

src/node/src/client.js

src/node/src/credentials.js

src/node/src/grpc_extension.js

src/node/src/metadata.js

src/node/src/server.js

src/node/test/call_test.js

src/node/test/channel_test.js

src/node/test/constant_test.js

src/node/test/end_to_end_test.js

src/node/test/server_test.js

templates/binding.gyp.template

templates/package.json.template