Issue 10 fix.

Date:       25 August 2013
Details:    The function cl_get_current_object() fails to check if there
            are any nodes in the CLL before accessing node members. If
            there are not, it should return CL_EMPTY.
File:       cllist.c
Line:       260
Branch:     master
Priority:   High
Resolved:   25 August 2013
Circular buffer library added.

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