Refine build scripts and modernize source code

[yaito3014]

Refactoring Todo

• Add constexpr to all functions (need careful investigation)
• Change static const local variables to non-static constexpr
• Replace const with constexpr
• Change unscoped enum to scoped
• Add noexcept
• Add [[nodiscard]]

[yaito3014]

Should we consider primitive iterator operations as noexcept? Standard doesn't really specify how iterators handle exceptions. If we are going careful way, we should create nothrow meta-functions for those operations.

[saki7]

Should we consider primitive iterator operations as noexcept? Standard doesn't really specify how iterators handle exceptions. If we are going careful way, we should create nothrow meta-functions for those operations.

Check out the actual implementation of <ranges>. They often use noexcept expression to strengthen functions.