Determine module search path order

[chunseoklee]

Nodejs search for a module in the order of
(1) ./node_modules
(2) $NODE_PATH/node_modules
(3) $HOME/node_modules
(4) $HOME/node_libraries
(5) (node execpath)/node/lib

We need to determine the search order w.r.t. multiple plaforms since enviroment or cwd is not available in small devices.

[chunseoklee]

current iotjs search path is documented in Module API

[seanshpark]

Good

[yichoi]

Closing since #417 merged.

Maybe we should re-consider the path with node in it. (in another issue)