Classes related to jEdit's TextArea.

Since jEdit 4.2, many TextArea classes have been split into a base and derived class. This is an attempt to make an API partition for the standalone text area. So for example:

- @ref JEditBuffer and @ref Buffer were split into two classes.
- @ref MouseHandler and @ref TextAreaMouseHandler were split.
- @ref TextArea and @ref JEditTextArea were split.
- @ref StandaloneTextArea is a new class for other open source Java applications to reuse.
- @ref JEditEmbeddedTextArea is a new class for jEdit plugins to reuse.

## Keeping things separate

The embeddable TextArea includes the packages "textarea", "buffer", "syntax", and should include nothing else. This means that for the standalone and abstract base classes, we should only use classes from that set.

To build the standalone textarea, "ant build-textArea", and you'll quickly see if you broke something by using a class that was not supposed to be used.