Update year of copyright in LICENSE.TXT files

This commit updates from 2012 to 2013 the year of copyright in
all license files.
Fix buffer problems and improves style of ns2 adapter

This commit make the following changes to the ns-2 component:
 * Fixes a problem that make the creation of a Tcl script fail if
   buffer sizes were not specified in the topology.
 * Corrects defects that made assignments of buffer in undirected
  topologies incorrect.
 * Makes the code compatible with Python 3 and improves the style
   in general.
 * Adds a Makefile to create a dist package out of the script.
Remove broken links to LICENSE files in README files

When displayed in GitHub page, the links to LICENSE.txt files
were broken. This commits removes these links.
Initial commit of the C++ API

This commit adds the initial version of the C++ API.

This commits contains the source code, the Makefile, required
external libraries, an example and the Doxygen configuration file
for generating the documentation.

In the README and in the Makefile there are references to test code
which is not part of this commit and that will be added later.
Add Java NamedPropertyContainer class.

This commit adds a new Java class called NamedPropertyContainer
and makes the Application and ProtocolStack classes inherit from it.

It also adds a hasProperty method to the PropertyContainer class.
Fix minor typos in core component files.
Updates Makefiles and .gitignore

This commit updates the core Makefile and create a global Makefile
which builds code and documentation of all components and collects
them in a centralized directory.

It also updates .gitignore accordingly.
Remove default constructor of Java of TrafficMatrix

This commits removes the default constructor of Java TrafficMatrix
class because it allowed users to create a TrafficMatrix object
without specifying the volume unit which remained null.

This commits also modifies all classes which used the default
constructor.
Add Java methods for validating and converting distance units

This commits adds method for validating distance units, used
for nodes geolocation and link lengths.
Fix duplicated edges problem in Java Topology.getAllEdges()

If a topology is undirected The Topology.getAllEdges() was
returning each edge twice, first in the form (u,v) and then in
the form (v, u). This commit prevents this from happening again.

It also fixes Topology.clone() method which was deep-copying nodes
and edges.

This commit also includes new test cases validating the features
added.