YafaRay v3.5.0 (2020-07-10)

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* IMPORTANT: Removal of *all* Boost dependencies. I've implemented new Unicode File management and new ImageFilm/PhotonMap saving/loading system.
   - All functionality depending on Boost has been rewritten from scratch to be able to remove Boost altogether.
   - Implemented Unicode UTF8/UTF16 conversions for strings in POSIX and Windows systems
   - Implemented Unicode UTF8/UTF16 file handling classes for Unicode paths in POSIX and Windows systems
   - In the process of that implementation I fixed some issues that were pending for a long time:
        - Now almost all files (including logs) are handled with the new file_t interface, so all works when using Unicode paths (logs were not correctly saved sometimes in Windows)
        - No longer need for temporary files when using OpenEXR files with Unicode paths.
   - Implemented new system to save / load ImageFilm and Photon Maps. The files generated with previous versions of YafaRay are *no longer valid* for this new method.
        - I think the new system is faster and generates smaller files (still big, depending on the amount of info)
        - Only drawback for now, when loading photon maps it has to regenerate the photon search KD tree, which is no longer saved in the photon map file.
        - No longer need to have a separate binary/text format for portability. In principle it should work the same in Linux/Windows, etc.
        - Endianness could be an issue for non-Intel/AMD platforms like ARM, to be investigated in the future, but that's a problem for another day.
   - Removed all SysInfo Boost code and replaced it by a "CMake-building" generation. Renamed sysinfo classes as build_info.

* IMPORTANT: CMake: made LibXML2 / ZLib optional. New CMake flag "WITH_XMLImport" to enable LibXML2. Now all the dependencies are finally optional and pure YafaRay library can be built without any dependencies.
* IMPORTANT: general header files de-coupling and cleanup, some old unused and broken code deleted
* Changing documentation extension to Markdown *.md
* Bidirectional integrator: adding integrator information to log and badge
* Bidirectional integrator: fixed transparent shadows, as requested in https://github.com/YafaRay/Blender-Exporter/issues/38
* SPPM: fixed memory corruption when using startx, starty not zero, as requested in https://github.com/YafaRay/Blender-Exporter/issues/41 and https://github.com/YafaRay/Blender-Exporter/issues/40
* XML Parser: added XML SAX parsing error diagnostic messages, as requested in https://github.com/YafaRay/Core/issues/121
* Added back -pthread flag for gcc/g++ compilation to fix FreeBSD builds To fix FreeBSD build as requested in https://github.com/YafaRay/Core/issues/113
* Removed some warnings for GCC. Also removed some Clang warnings as requested by https://github.com/YafaRay/Core/issues/110
* Fixed some source file comments license boilerplate to remove wrongly encoded characters that were confusing some IDEs
* CMake: unifying all cmake-generated headers, simplifying code. Threads: moved runtime detection to dedicated class
* OpenCV Denoise: better encapsulation and code reuse, at the expense of slower processing
* Renamed yafsystem/sharedlibrary_t by a (clearer) dynamic_library/dynamicLoadedLibrary_t
* Git: added .gitignore to ignore all "hidden" files starting with "." (i.e. IDE generated files)
* Swig Ruby: avoid -Wsign-compare warning.