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.
There is no good reason to not support it from `compileTemplateFiles`, technically it could starts a watcher to the input array the same way it does for the input dir on `compileTemplates`.

This pull request intention was to expose `compileTemplateFiles` with minimal changes in the existing code, eventually the functionality could be added.

What do you prefer?