exchange 'npm link' with symbolic link solution

* additional dependencies: execSync & underscore
* support options.dir as an Array of different paths to linkDependencies
* linker
 ** exec - support also functions as elements of 'cmds'
 ** use symbolic links/junctions instead of 'npm link'
* link_helper
 ** remove to use of baseDir as far as possible
 ** baseDirs is an Array of Paths