Add maximum matching algorithm for weighted graphs

[Tamás Nepusz]

A possible O(|V|*|E|*log(|V|)) algorithm can be found in:

Zvi Galil, Efficient algorithms for finding maximum matching in graphs, ACM Computing Surveys, 1986.

A Python implementation of the algorithm is here: http://www.xs4all.nl/~rjoris/maximummatching.html
There's also a C implementation: ftp://dimacs.rutgers.edu/pub/netflow/matching/weighted/solver-1

[Tamás Nepusz (ntamas)]

Note: the C implementation above is O(|V|^3), so it's better suited for small dense graphs. It is an implementation of the following algorithm:

H.J. Gabow, Implementation of algorithms for maximum matching on nonbipartite graphs, Stanford Ph.D thesis, 1973.

[Gábor Csárdi (gabor.csardi)]

The development of igraph has moved to github, so please do not comment on this bug here. You are of course welcome to comment on github, here:
https://github.com/igraph/igraph/issues/321