Fix handling of node coordinates and make distance units tunable

This commit fixes the handling of node coordinates in Abilene and
Topology zoo parsers. Before, node coordinated were treated as if
they were expressed in kilometers, instead of degrees, thus leading
to incorrect link length calculation and hence incorrect delay
calculation based on node geodistance.

In addition, this commit makes it possible to specify the distance
unit of link lengths and node coordinates of Waxman and BRITE
topologies.

In summary this commit does the following:

* Correct calculation of link distance in Topology zoo and Abilene
  topologies
* Make distance unit tunable in Waxman and BRITE topologies
* Add calculation of link lengths of Inet topologies at parsing stage
* Edit set_delays_geo_distance function to work properly with link
  lengths expressed in various distance units.
* Change documentation to clarify when node attributes longitude and
  latitude are expressed in degrees or not.

With this commit, set_delays_geo_distance is no longer able to
calculate link delay only based on node coordinates without
precalculated link length because of node coordinate unit ambiguity
(degrees or metric units). This might be improved by a later commit.
Improve set_capacities_random_power_law function

This commit improves the function assigning link capacities according
to a power law distribution. Before this commit, this function
assigned capacity so that the product of capacity value and
probability that a link has that capacity is constant, i.e. the
skewness parameter of the power-law relationship was fixed to 1.

After this commit, capacity value and probability have a power-law
relationship with tunable skewness.
Fix minor typos around the code

This commit fixes minor typos in the code and documentation.
Improve Java support for link length attribute

This commit improves the handling of link length attributes performed
by the Java component.
Add addEdge method with implicit Edge instatiation in Java component

This commit adds a new addEdge method to the Topology class of the
Java component which only requires to specify endpoints and
automatically instantiates an Edge object.
Change default values of Java Edge object attributes

This commit changes the default value of some attributes of the Java
Edge object
Change version number to 0.3.2