Remove swap file
Start basing pginfo on boost graph
Fix file I/O to boost graph
First attempt to use BFS algorithm in BGL
Add basic version of diameter computation.

Warning: does not currently work.
Reimplement all other algorithms, except alternation depth and k-neighbourhood.

This implementation is built upon boost graph.
The alternation-depth algorithm will not be reimplemented in its current form,
since the definition does not correspond to the ones found in the literature.

TODO:
* Clean up the implementations
* Add implementation for k-neighbourhood
Generalise some algorithms to arbitrary graphs
Implement additional algorithms.

* Added k-neighbourhood (with min, max, avg)
* Added computation of min,max,avg in- and out-degree.
* Cleaned up the implementation to be more in line with boost graph
Merge branch 'wip/boost' of https://github.com/jkeiren/pginfo into wip/boost