Create example code for various use cases of ABCL

[vvoutilainen]

It would be useful to have example code so that we can point
new people to actual, working examples. The previous discussion
on the mailing list have been vague at best, and sometimes
even gave incorrect advice.

The following cases should be shown in the examples:

1) calling lisp code from java code
2) calling java code from lisp code
3) implementing a java interface in lisp code

[vvoutilainen]

Additionally, the first version of the examples will show how to
define a new java class (extending an existing class) in lisp code.

After that part is done, more examples will be created to show how
to handle java exceptions in lisp (when calling java code from lisp code)
and how to handle lisp conditions in java (when calling lisp code from
java code)

[vvoutilainen]

Initial version committed in revision 11382. The class definition is not added yet,
runtime-class.lisp doesn't seem to be part of abcl build.

[vvoutilainen]

The commit r11385 adds a simple handling of a java exception. Lisp condition
handling in java code is still missing, but it's not going to be added at this
point.