Fix rounding problem in _set_capacities_proportionally

This commit fixes a defect in core library function
_set_capacities_proportionally which was sometimes failing to assign
a capacity to the link with the greatest metric value due to float
rounding issues. This occurred particularly when using
communicability centrality gravity as metric.
Fix minor style issues in documentation and comments

This commit fixes some minor style issues in documentation and
comments
Change style of __all__ attributes in core library
Replace list comprehension with iterators where possible

This commit replaces lists comprehension with iterators throughout
the source and test code of the core library.

These changes speed up code execution and reduce memory footprint.
Fix issue with EventSchedule __add__ method

EventSchedule __add__ method used to return a NoneType rahter than an
EventSchedule object. This commit fixes that problem.
Minor optimization of trafficmatrices module

This commit adds some minor code optimization to the code of the
trafficmatrices module of the core library.
Add test cases to core library

This commit adds test cases to the core library test suite. Now all
functions and class methods are covered by at least a test case.
Add support for link weights and simplex links in ns-2

This commit adds support for link weights parsing in the ns-2 adapter

It also changes the behaviour in case of directed topologies. Now,
links of directed topologies are parsed as simplex links as opposed
to duplex links.
Minor refactoring of fnss-troubleshoot script
Minor fix in dist target of ns-3 Makefile

The dist target of ns-3 Makefile used to fail because the dist
directory was include in the zip file. Now it is excluded and this
fixes the problem.