Issue 4 fix.

Date:       21 August 2013
Details:    Incorrect return values used in de_get_first_object(),
            de_get_last_object(), de_set_limit(), and de_destroy().
File:       deque.h
Line:       214, 230, 261, 268
Branch:     master
Priority:   Low
Resolved:   21 August 2013
Issue 5 fix.

Date:       21 August 2013
Details:    Incorrect return value used in de_destroy().
File:       deque.c
Line:       270
Branch:     master
Priority:   Low
Resolved:   21 August 2013
Issue 6 fix.

Date:       21 August 2013
Details:    No mention is made in de_set_limit() of setting the
            node limit to zero to disable it and let the deque
            grow without limit.
File:       deque.h
Line:       261
Branch:     master
Priority:   Low
Resolved:   21 August 2013
Queue library added.

1.  Added the queue library and its test unit. This provides full
    coverage of the queue codebase, with the exception of testing
    QU_NO_MEMORY function return values.