filling in most of the jsdocs for GetFastValue and SpriteSheetFromAtlas

Author: Evan

src/textures/parsers/SpriteSheetFromAtlas.js

@@ -8,17 +8,23 @@ var GetFastValue = require('../../utils/object/GetFastValue');
 
 /**
  * Parses a Sprite Sheet and adds the Frames to the Texture, where the Sprite Sheet is stored as a frame within an Atlas.
- * 
+ *
  * In Phaser terminology a Sprite Sheet is a texture containing different frames, but each frame is the exact
  * same size and cannot be trimmed or rotated.
  *
  * @function Phaser.Textures.Parsers.SpriteSheetFromAtlas
- * @memberOf Phaser.Textures.Parsers
+ * @memberof Phaser.Textures.Parsers
  * @since 3.0.0
  *
  * @param {Phaser.Textures.Texture} texture - The Texture to add the Frames to.
  * @param {Phaser.Textures.Frame} frame - The Frame that contains the Sprite Sheet.
- * @param {object} config - [description]
+ * @param {object} config - An object describing how to parse the Sprite Sheet.
+ * @param {number} config.frameWidth - Width in pixels of a single frame in the sprite sheet.
+ * @param {number} [config.frameHeight] - Height in pixels of a single frame in the sprite sheet. Defaults to frameWidth if not provided.
+ * @param {number} [config.startFrame=0] - [description]
+ * @param {number} [config.endFrame=-1] - [description]
+ * @param {number} [config.margin=0] - If the frames have been drawn with a margin, specify the amount here.
+ * @param {number} [config.spacing=0] - If the frames have been drawn with spacing between them, specify the amount here.
  *
  * @return {Phaser.Textures.Texture} The Texture modified by this parser.
  */

src/utils/object/GetFastValue.js

@@ -4,21 +4,17 @@
  * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
  */
 
-//  Source object
-//  The key as a string, can only be 1 level deep (no periods), must exist at the top level of the source object
-//  The default value to use if the key doesn't exist
-
 /**
- * [description]
+ * Finds the key within the top level of the {@link source} object, or returns {@link defaultValue}
  *
  * @function Phaser.Utils.Object.GetFastValue
  * @since 3.0.0
  *
- * @param {object} source - [description]
- * @param {string} key - [description]
- * @param {*} [defaultValue] - [description]
+ * @param {object} source - The object to search
+ * @param {string} key - The key for the property on source. Must exist at the top level of the source object (no periods)
+ * @param {*} [defaultValue] - The default value to use if the key does not exist.
  *
- * @return {*} [description]
+ * @return {*} The value if found; otherwise, defaultValue (null if none provided)
  */
 var GetFastValue = function (source, key, defaultValue)
 {