This commit contains all the changes that were implemented over a large number of commits on the branch
feature/mindquantum-cxx. These changes include:

* Build scripts *

Complete rewrite of building scripts to make them more usable and customizable going forward.

- Added
  + `build.ps1` Python wheel building script
  + `build_locally.ps1` local building script
- Updated
  + `build.bat` Python wheel building script
  + `buid.sh` Python wheel building script
  + `build_locally.bat` local building script
  + `buid_locally.sh` local building script

* CMake *

Complete rewrite of the CMake build system for increased reliability and maintainability

- Added
  + Support for installing MindQuantum as a local package/library
  + Third-party library sub-directory with CMake functions/macros to easily manage third-party libraries and
    dependencies
  + New standard way of finding packages using CMake
  + Support for Nvidia NVHPC in preparation for upcoming GPU backend
  + Building of documentation using CMake (if `sphinx-build` can be found)
- Updated
  + Changed minimum CMake version to 3.20 (can be installed via `pip` on most platforms or use the build scripts)
  + Moved all C++ code (except tests) into `ccsrc` sub-directory
  + Updated existing CMake package finding code
  + Better handling of compiler/linker flags
  + Improved RPATH/RUNPATH test

* C++ *

- Added
  + New C++ backend (still a work in progress) in `ccsrc/cxx_experimental`

* Python *

- Added
  + New C++ backend support code (still a work in progress) in `mindquantum/experimental`
  + `mindquantum-config` package to allow Python users to easily locate the location of the installation configuration
     files
  + Support for `extras_require` when installing MindQuantum
- Updated
  + All Python code now passes `flake8` tests with no warnings
  + Update `pyproject.toml` configuration file
  + Update `setup.cfg` configuration file
  + Update `setup.py` to allow for more flexibility in passing CMake variables
  + Improved wheel delocation in custom build backend

* Repository *

- Added
  + `pre-commit` configuration files (with versions for both GitHub and Gitee repositories)
  + `yamllint` configuration file
  + Configuration file for ReadTheDocs automatic documentation generation
  + `INSTALL.md` file to help new users build MindQuantum
  + `cpplint` configuration files
  + `linklint` filter file
- Updated
  + Update `clang-format` configuration file
  + Update `cmake-format` configuration file
  + Update `codespell` configuration file

* GitHub *

- Added
  + Configuration file for GitHub repository
    * Added builds for most common compilers and operating systems

Co-authored-by: Dmitry Mikushin <dmitry.mikushin@huawei.com>
Signed-off-by: Damien Nguyen <damien1@huawei.com>