add get wrapper argument to transform and generator callbacks

API.md

@@ -72,7 +72,7 @@ Returns the `Defiler` instance for chaining.
 
 Register a new transform to be applied to all files.
 
-- `transform(file)` - a transformer function, which is passed a `File` instance to mutate. In your function, `this` will be the current `Defiler` instance. The function can return a `Promise` to indicate when it's done
+- `transform(file, get(path))` - a transformer function, which is passed a `File` instance to mutate; it is also passed a function `get(path)` which calls the `get(path, dependent)` method (see below) with the appropriate `dependent` (that is, the current file's path), as a convenience. In your function, `this` will be the current `Defiler` instance. The function can return a `Promise` to indicate when it's done
 - `if(file)` - _(optional)_ a function that, if present, will be called with the `File` instance before calling the main `transform`. In your function, `this` will be the current `Defiler` instance. If the function returns `false` or a `Promise` resolving to `false`, the transform is skipped
 
 Returns the `Defiler` instance for chaining.
@@ -82,7 +82,7 @@ Returns the `Defiler` instance for chaining.
 Register a new generated file, not directly sourced from a physical file.
 
 - `path` - the relative path of the file to register the generator for
-- `generator(file)` - a function that is passed a new `File` instance containing only a path, which it should then mutate.  In your function, `this` will be the current `Defiler` instance. The function can return a `Promise` to indicate when it's done
+- `generator(file, get(path))` - a function that is passed a new `File` instance containing only a path, which it should then mutate; it is also passed a function `get(path)` which calls the `get(path, dependent)` method (see below) with the appropriate `dependent` (that is, the current file's path), as a convenience.  In your function, `this` will be the current `Defiler` instance. The function can return a `Promise` to indicate when it's done
 
 Returns the `Defiler` instance for chaining.
 
@@ -109,6 +109,8 @@ This can be asked for physical or generated files. If you ask for one or more ph
 
 If a path `dependent` is passed, `dependent` is registered as depending on the file or files in `path`. When the file or files in `path` change, the file at `dependent` will be automatically re-transformed (using `refile`, below). If you're calling `get` inside a transform or generator, `dependent` should typically be the path of the file you're transforming or generating.
 
+Typically, you would not call this directly, and would instead call the function passed as a second argument to the transform or generator callback, which then calls this method with the appropriate `dependent`.
+
 ### `refile(path)`
 
 Manually re-transform a `File`. This can be from a physical file or a generated one. Returns a `Promise` to indicate when all processing is complete. Re-transforming a physical file will use the version of it that was last read into memory. Re-transforming a generated file will call its generator again.