Implement the 'autoSize' option of the TextShape object.
This change is the initial implementation of the 'autoSize' option, which automatically changes the size of a TextShape object to fit its text. Unfortunately, this change does not automatically invalidate the rectangle of the TextShape object and the caller must invalidate it.
Merge pull request #35 from tkihira/hbono/add-autosize

Implement the 'autoSize' option of the TextShape object.