Replace Boost::foreach dependency with range-based for

[georgthegreat]

While the library is still marked as c++03 compatible I wonder if the time has come to follow the rest of the boost libraries and raise it up to c++11.

[Osyotr]

These public dependencies require C++11:

• Boost::align
• Boost::bind
• Boost::conversion
• Boost::function
• Boost::iterator
• Boost::lexical_cast
• Boost::smart_ptr

It is perfectly reasonable to drop C++03 support in Boost::python, too.

[e-kwsm]

python/.github/workflows/test-ubuntu.yml

Line 14 in 4fc3afa

std: [c++98, c++11, c++14, c++17]

drop c++98?