Mass bind -> lambda conversion

See merge request !30

Source file work done with custom-modified versions of clang-format
and clang-tidy, via the modernize-avoid-bind checker. Headers were
modified by hand. A script removed uses of <functional> and <boost/bind.hpp>.

This implements buffered io, instead of loading the entire edge list to memory.

Allow graph_tool.draw.draw_hierarchy to be used without GTK installed

See merge request !29

Remove boost::any wrapper around std::shared_ptr

See merge request !28

Remove const qualifier from object that can be modified

See merge request !27

std::shared_ptr provides a limited amount of type erasure natively
based on void* and the fact that it stores the original type in the
deleter. As a result, if you know the original type, you can call
std::static_pointer_cast and recover a legitimate shared_ptr of the
right type, very efficiently.

It looks like the use of boost::any in this code is:

1) to hide the pointed-to type so a uniform container can be used
2) to represent "no pointer"

both of which can be handled natively by shared_ptr<void> with a small
performance gain from removing one indirection.

Mark PythonEdge as "final" per clang-tidy

See merge request !26