Periodogram example

Added periodogram example, tidied up some IDE specific files and tidied up submodules.

CI

• Added CI through github actions

• CI runs clang-tidy and ASAN

• CI builds on Windows, Linux, macOS

• Algorithm does not throw (except std::exceptions)

• Improved comments

• Improved CMake build system

• Improved tests

Version 0.1

• Improved interface, more practical use case for user-defined vector type.
• Tests implemented in Catch2, runnable with CTest.
• Modern CMake structure.