Custom filesystem support

[fboranek]

MR is ready to review these features:

• fixed version of Dano MR Add FilesystemInterface_t support
• added support for Python as well
• moved handling relative / absolute path from several places into file system implementation
• added tests

[burlog]

Hi,

I've some general objections to your pull request.

• it contains plenty coding style changes that's not needed - remove them please,
• you added one more testing framework - it's rather general objection, there is Google Test tests now and you should use it. I know that they are disabled but we wan't do things better, don't we? But on other side for Teng3 I rewrite all tests to Catch2 in BDD style. It may be nice if you rewrite test to Catch2 either but I will be satisfied if you left them in Boost Test.
• you made Teng depended on Boost library - remove it please (use std::hash instead).

I've some other minor objections also which we can discuss after you fix all of I mentioned above.

[fboranek]

• it contains plenty coding style changes that's not needed - remove them please,

done

• you made Teng depended on Boost library - remove it please (use std::hash instead).

Yes, I added the dependency on boost, but it just a compile dependency. std::hash is since C++11 and it doesn't occur to me that the project uses C++11. I enable C++14 just on tests, actually, the tests are compiled and run only if C++14 is available. If you are ok with an upgrade to C++11 a can use the standard library.

• you added one more testing framework - it's rather general objection, there is Google Test tests now and you should use it. I know that they are disabled but we wan't do things better, don't we? But on other side for Teng3 I rewrite all tests to Catch2 in BDD style. It may be nice if you rewrite test to Catch2 either but I will be satisfied if you left them in Boost Test.

It looks very similar. It seems to me it better rewrite it in your branch. I will gladly do that. For now let's stick with boost.

[burlog]

Let's enable C++11. It should be ok.

[fboranek]

Done.