Adds the KillRing class and its test.
Adds support for the yank and yank pop operations using the KillRing class to keep the killed text.
Avoid falling in never ending loop in edge cases where the kill word or kill word backwards are invoked when the buffer is empty.
Added a new method addBackwards to adds text to the kill ring product of a 'backwards' kill. This permits that consecutive backwards operations or combination of mixed backwards and forward kills to leave the ring in a correct state. Previously if you had 'hi there' and did backward-kill-word twice followed by a yank the result was 'there hi'.
Adds support to preserve in the kill ring the text removed after a UNIX_LINE_DISCARD or UNIX_WORD_RUBOUT operations.
Added a bunch of new tests using the ConsoleReaderTestSupport infrastructure.
Merge branch 'pulls/94'