Upgrade: linklist.h

reverse printing added.
Upgrade: linklist

    Rotating function added.

Upgrade: gitignore

    ignore the output file.
Upgrade: makefile

Added new file: sortedlinklist.h
Added: sortedlinklist.h

skeleton of the new class.
Upgrade: makefile

    new target 'check' to check the output file from program.
    new variable 'OUTPUT_FILE', redirect the output to file, easy to read.
    modify target 'run', add a dependency on the executable file.
Upgrade: node.h

    new function: newnode(value)
        return a new node with a value.

Upgrade: linklist.h

    adjust the parameter to be inherited.

Upgrade: sortedlinklist.h

    new function: append
    append the new element in sorted position.