* Add Case conversion functions to the article
These functions tell the programmers about converting their string data type value either into upper case letters or lower case letters.
* Fix formatting and phrasing
Using `==` to compare String objects checks references to the two objects, and in this case, those two references point to the same string object created **in the String Pool**. Hence this returns `true`, and not `false`, as is incorrectly stated in the guide.
Also fixed formatting.
