This fixes issue #258.

This fixes issue #57 (again).

Use int64_t instead of int32_t as the default label type.

This introduces support for returning a generator in
subgraph_isomorphism(), so that all matches do not need to be kept on
memory simultaneously.

This fixes issue #255.

This facilitates the development of C++ extensions to graph-tool.

This improves the consistency in the documentation.

This fixes issue #252.

This revers the dependency to 1.54. This can be done since
boost::coroutines has been made optional.

This causes the test to fail when only static variables are available.

This reduces even more compilation time and memory use.