Up requirements of Boost and C++

[robe2]

Boost 1.56 is very old.

Right now our docs have

C and C++ compilers

• Compiling with Boost 1.56 up to Boost 1.74 requires C++ Compiler with C++03 or C++11 standard support
• Compiling with Boost 1.75 requires C++ Compiler with C++14 standard support

1.75 was introduced in 2019. I propose get rid of support of Boost < 1.75 and require C++14.

We already voted and now require C++17 for pgRouting 4.0

Also change the docs:

C and C++ compilers

• Minimum C++ for pgRouting is C++17
• Compiling with Boost 1.75 requires C++ Compiler with C++14 standard support

[ayushjariyal]

@robe2, I want to work on this issue. Could you please assign it to me?