* CMakeLists.txt: bump C++ standard from 14 to 17
* .travis.yml: bump xcode from 8.3 to 11.2
* .appveyor.yml: bump Visual Studio from 2015 to 2017
* README.md: bump various versions related to #650
* CHANGELOG.md: fix#650, add entry for #650.
* deps/llvm: do not use LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN
This was necessary only for builds on older MS Visual Studios (e.g. 2015).
These are no longer supported by RetDec - Visual Studio 2017 is minimum.
* appveyor+travis: temporarily enable builds of this branch
* src: remove use of std::ptr_fun and std::not1.
These were either deprecated or removed in C++17.
* .travis.yml: do not upgrade python3
It is already installed and upgraded in the used xcode 11.2.
* depspelib: update reference to the c++17 PeLib version.
* deps/pelib: update reference to the latest commit in c++17
* deps/pelib: update reference to the latest c++178 fix
* deps/yaramod: update reference to v2.12.0
* deps/variant: replace with std::variant and remove
* deps/pelib: update reference to the latest master
* deps/yaramod: update reference to v2.12.1
* replace Maybe implementations with C++17 std::optional
* utils/filesystem_path: remove utils/value include
* add missing <optional> includes
* tests/capstone2llvmir: replace deprecated macros with new ones
replace INSTANTIATE_TEST_CASE_P with INSTANTIATE_TEST_SUITE_P
* tests/llvmir2hll: fix "assign to itself" warnings
* llvmir2hll/graphs: replace deprecated use of std::iterator
* .travis.yml: move from Ubuntu Xenial to Bionic
* deps/rapidjson: define RAPIDJSON_NOMEMBERITERATORCLASS
* plain and json getters
* plain json presentations
* dotnet class and reconstructor
* fileformat and related
* fileinfo and cmake
* minor changes - cleanup and docs
* DotnetClass linking fixed
* child nodes libname derivation fixed
* hash names type postfix added
* typeref index presentation removed
* hashes fixed
* std::variant alternative for cpp 11/14/17
* type check for DotnetClass
* Removed submodule file
* veriant as non gitmodule
* variant completely removed
* Variant reinstalled as non submodule
* Another deletion of submodule
* Another addition of non submodule variant
* variant single header
* branch rebase - variant single header
* variant hidden files deleted
* Cosmetic changes
