C interface/implementation

• Interface and implementation are now in C11.
• Support custom allocator.
• Support libc overrides.
• Modern CMake build system.
• Tests run with sanitizers.
• 100% code coverage.

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.