HPX 1.5.0 release candidate 1

The first release candidate of HPX 1.5.0 is now available. Get it by cloning the repository and checking out the 1.5.0-rc1 tag or downloading the archive from our releases page: https://github.com/STEllAR-GROUP/hpx/releases/tag/1.5.0-rc1.
                                                                                   
This is a big release with many changes and improvements. The main breaking change of this release is that HPX now requires a C++14 compatible compiler and the standard is set by default to C++14. Most relevant in terms of your builds is that we have refactored our CMake targets. You can now link to HPX::hpx (note the new HPX:: namespace) and if you need your main() to be defined as the first HPX thread, you will also need to link to HPX::wrap_main. We continued the modularization efforts which is still intended to be a non-breaking change. As part of the modularization we have moved many headers around. The old header locations will still work for a couple of releases but will cause warnings in your builds. We encourage you to update your includes to the new header locations as soon as possible. If you can’t update your includes just yet you can also turn off the warnings per module with the CMake option HPX_<MODULENAME>_WITH_DEPRECATION_WARNINGS=OFF. Otherwise, you can turn off the compatibility headers of the specific module with HPX_<MODULENAME>_WITH_COMPATIBILITY_HEADERS=OFF. While we believe weve sorted out most issues, we ask you to try out the release candidate and let us know of any issues that you find. In the first release candidate the APEX tag has not yet been updated to the latest version.

Please let us know of any issues, small or big, that you might find by opening an issue on GitHub: https://github.com/STEllAR-GROUP/hpx/issues.

A draft version of the release notes for HPX 1.5.0 will soon be opened on Github, we will link to it in the next release candidate.