[restructure] Restructure the core files
drwxr-xr-x - .ahub
-rw-r--r-- 2677 .clang-format
drwxr-xr-x - .github
-rw-r--r-- 316 .gitignore
-rw-r--r-- 0 .gitmodules
drwxr-xr-x - Applications
-rw-r--r-- 3333 CODE_OF_CONDUCT.md
-rw-r--r-- 2550 CONTRIBUTING.md
-rw-r--r-- 11364 LICENSE
-rw-r--r-- 1027 MAINTAINERS.md
-rw-r--r-- 14371 README.md
drwxr-xr-x - api
drwxr-xr-x - debian
drwxr-xr-x - docs
drwxr-xr-x - jni
-rw-r--r-- 4767 meson.build
-rw-r--r-- 794 meson_options.txt
drwxr-xr-x - nnstreamer
-rw-r--r-- 246 nntrainer.pc.in
drwxr-xr-x - nntrainer
drwxr-xr-x - packaging
drwxr-xr-x - test