Adding config.process method to process raw values already retrieved from config data.
Changing this.task.file somewhat.

* .dest is still template-expanded.
* .src is still a template-/file-expanded, flattened array.
* .srcRaw has been removed.
* .orig contains the normalized file object with .src, .dest, etc. properties
* The .orig.dest and .orig.src properties are not template-expanded.
* The .orig.src property is normalized to a non-file-expanded, flattened array.
Support .nonull in multi task file objects.
Support expandMapping declaratively within multi task files object.

* Set expand: true to enable.
* Supports all file.expandMapping options.
* Files are expanded at task-run-time, so filesystem changes post init-time will be recognized.
* Resulting this.file.orig property contains all properties of the original file object.
Adding --verbose logging for multi task src-dest mappings.
Removing file.expandFileURLs method as it's now obviated by the "nonull" option.
The file.expand method now supports a "filter" option.

* Its string value is the name of any method supported by fs.statSync, eg. 'isFile' or 'isDirectory'.
File mappings now support an 'ext' option to change file extensions.
Improving multi task test gruntfile error output via difflet lib.
Inside multi tasks, all templates (values, not keys) in this.data are automatically processed.

* "dest" key values will be automatically processed while being normalized in file objects.
Reverted changes made for gh-524.

* The previous abstraction, while nice, didn't allow for practical per-task setup/teardown. Instead of building further abstraction, I am reverting. This will be addressed in 0.5.
* Multi task functions are now run once per target, not once per file mapping object.
* Inside tasks, this.files is an array of fully normalized/expanded file mapping objects, each with .src .dest .orig properties (as appropriate)
* Inside tasks, this.filesSrc is a flattened, uniqued array of all this.files object .src properties.
* Task authors will be responsible for iterating over this.files or this.filesSrc to process files in their multi task.