Get dependencies using vcpkg

vcpkg can be used to simplify the process of getting all the dependencies. After cloning vcpkg, run the following command to install dependencies on Windows:

.\bootstrap-vcpkg.bat -disableMetrics
.\vcpkg.exe install --triplet x64-windows avisynthplus boost-asio boost-container boost-crc boost-filesystem boost-flyweight boost-gil boost-interprocess 'boost-locale[icu]' 'boost-regex[icu]' boost-scope-exit boost-thread fftw3 hunspell icu libass libiconv uchardet wxwidgets gtest

FFMS2 and XAudio2redist still need manual installation at this time. Follow corresponding sections in https://github.com/wangqr/Aegisub/wiki/Compile-guide-for-Windows-(CMake,-MSVC) to get them.

To use vcpkg in CMake, select Specify toolchain file for cross-compiling during configure, and choose vcpkg/scripts/buildsystems/vcpkg.cmake as the toolchain file. If you want to make a release build, delete the vcpkg\installed\x64-windows\debug folder before running CMake.