Configure WhiteSource Bolt for GitHub - #1

…changkun#322)

Add a new section 2.7 covering three self-contained C++17 language
features that were missing (tracked in #1):
- inline variables (incl. in-class static member init)
- nested namespace definitions (namespace A::B::C)
- constexpr lambda

Each has a runnable example mirrored under code/2 and verified to
compile and run with clang++ -std=c++2a -pedantic.

Refs #1

The diagnostic message of static_assert became optional in C++17.
Add a subsection in 2.7 with a compiled example (code/2/2.24). Refs #1

Explain that copy elision when initializing from a same-type prvalue
became mandatory in C++17, so returning a non-copyable/non-movable
prvalue by value is now well-formed. Compiled example in code/3/3.8.
Refs #1

New section 4.4 introduces the non-owning read-only std::string_view
(with a lifetime caveat) and the non-arithmetic std::byte raw-memory
type. Compiled examples in code/4/4.4 and code/4/4.5. Refs #1

Replace the TODO stub with a full chapter on std::filesystem (C++17):
path construction/decomposition, status queries (with error_code vs
exception handling), directory iteration (directory_iterator and the
recursive variant), and create/copy/remove operations. Includes a
self-contained, runnable example (code/8/8.1) that works in a scratch
directory under the temp path; verified to compile and run with
clang++ -std=c++2a. Refs #1 changkun#269

Add subsections in 2.7: aggregates may now have aggregate base classes
and be brace-initialized through them; and std::conjunction/disjunction/
negation for composing type traits. Compiled examples code/2/2.25-2.26.
Refs #1

Section 4.5 covers try_emplace / insert_or_assign and node-based
extract / merge; section 4.6 introduces polymorphic allocators
(std::pmr) with a monotonic_buffer_resource example. Compiled examples
code/4/4.6-4.7. Refs #1

Extend 9.4 with dynamic allocation of over-aligned types: C++17 added
operator new/delete overloads taking std::align_val_t, so new respects
alignof for over-aligned types. Compiled example code/9/9.4. Refs #1

Section 9.5 explains why reinterpret_cast-based type punning is UB
(strict aliasing) and shows the correct std::memcpy and C++20
std::bit_cast approaches (compiled example code/9/9.5). Section 9.6
documents the C++17 special math functions, with an explicit caveat
that libc++ historically lacks them (so no compiled example). Refs #1

Add a 2.7 subsection on __has_include for portable conditional header
inclusion, with a compiled example (code/2/2.27). Refs #1

Replace the TODO stubs in the C++20 chapter with real content:
- Concepts: a concrete, compiled requires-expression example
- Modules: export/import syntax, with a note that it needs a
  module-aware multi-step build (not the repo one-liner)
- Ranges: lazy filter|transform pipeline (compiled, code/10/10.3)
- Coroutines: a minimal co_yield generator (compiled, code/10/10.4)
- Correct two factual errors: Contracts were removed from C++20
  (now targeting C++26, see changkun#318) and Transactional Memory is only a
  TS, never part of C++20; they are no longer presented as C++20.

Refs #1

Replace the TODO stubs with concrete, widely-accepted best practices
across tools, coding style, performance, safety, maintainability, and
portability. Reword the intro to reference the C++ Core Guidelines and
frame the content as generally accepted practice rather than secret
tips. Refs #1