Adds support to compiles and loads all `.soy` files from array

Currently soynode only allows to compiling templates from an input directory, expose `soynode.compileTemplateFiles(dir, callback)` in order to allow compile from files array.
options.inputDir is global state; overwriting here will cause lots of bugs when the API is called multiple times. i think you still need to parameterize inputDir so that the value is captured.