Dev to master

• Several formatting changes, including

  • apply Google-style clang-format to src and benchmark folders (#49 (closed))
  • strip trailing whitespace (#82 (closed))
  • apply cpplint to src
  • remove most relative include paths (#81 (closed))

• Modernize c++, including

  • use auto for dynamic_cast and dynamic_pointer_cast (#87 (closed))
  • use make_shared for shared_ptr (#86 (closed))
  • remove using namespace from core header file (#83 (closed))
  • use nullptr instead of NULL (#84 (closed))

• To prevent regression:

  • added .pre-commit-config.yaml to prevent regression
  • TODO: enable on CI pipeline

• Future improvements:

  • enable sorted headers in clang-format
  • fix copyright to pass more cpplint checks
  • fix more uses of new => make_shared (e.g. LPPriveKey, Ciphertext, etc.)