VS 2019 16.5

• Hello, world!
  • Announced this repo at CppCon 2019.
  • Added initial documentation: readme, license, and roadmap.
  • Added initial CMake build scripts for Desktop-only msvcp. #5 #80 #98 #101
  • Investigated continuous integration options, like GitHub Actions or Azure Pipelines. (Chose Azure Pipelines.)
  • Automated builds running in PRs. #114
  • Investigated test harness solutions, either building our own to more closely match the internal system in a reasonable way, or using libcxx's lit. (Chose to use lit.)
  • Began auditing test case source files from the std and tr1 test suites.
  • Implemented Custom Autolinks in this repo.
• Merged C++20 features:
  • P0325R4 #135 to_array()
  • P0340R3 #284 SFINAE-Friendly underlying_type
  • P0356R5 #158 bind_front()
    • P1651R0 bind_front() Should Not Unwrap reference_wrapper
    • LWG-3184 Inconsistencies in bind_front wording
  • P0439R0 #124 enum class memory_order
  • P0553R4 #310 <bit> Rotating And Counting Functions
  • P0556R3 #310 <bit> ispow2(), ceil2(), floor2(), log2p1() bit_length()
    • P1355R2 Narrow Contract For ceil2()
  • P0595R2 #353 is_constant_evaluated()
  • P0631R8 #261 <numbers> Math Constants
  • P0655R1 #201 visit<R>()
  • P0738R2 #246 istream_iterator Cleanup
  • P0767R1 #179 Deprecating is_pod
  • P0966R1 #176 string::reserve() Should Not Shrink
  • P1209R0 #236 erase_if(), erase()
  • P1227R2 #130 Signed std::ssize()
  • P1357R1 #127 is_bounded_array, is_unbounded_array
  • P1612R1 #305 Relocating endian To <bit>
  • P1690R1 #341 Refining Heterogeneous Lookup For Unordered Containers
  • P1902R1 #287 #353 Missing Feature-Test Macros 2017-2019
  • P1959R0 #381 Removing weak_equality And strong_equality
• Merged partial C++20 features:
  • P0896R4 #82 #84 #91 #93 #95 #329 #352 Ranges
  • P1614R2 #242 Adding Spaceship <=> To The Library
• Merged LWG issue resolutions:
  • LWG-2899 #193 is_(nothrow_)move_constructible and tuple, optional, and unique_ptr
  • LWG-3158 #195 tuple(allocator_arg_t, const Alloc&) should be conditionally explicit
  • LWG-3199 #353 istream >> bitset<0> fails
  • LWG-3257 #353 Missing feature testing macro update from P0858
  • LWG-3266 #353 to_chars(bool) should be deleted
• Merged proposed resolutions for LWG issues (not yet accepted for the C++ Working Draft, but we've chosen to implement this speculatively):
  • LWG-3268 #151 memory_order::memory_order_meow broken in C++20
• Fixed bugs:
  • Restored swap(unique_ptr&, unique_ptr&) which was mistakenly removed. #170
  • When erasing an empty range in a vector, avoided self-move-assigning all elements. #228
  • Removed a noexcept that was incorrectly applied to an allocating helper function in list. #77
  • valarray now uses argument-dependent lookup when calling sin(), cos(), pow(), sqrt(), etc. as required by the Standard. #286
  • Fixed <filesystem> linker errors for UWP developers. #356
  • Changed the return type of locale's assignment operator to const locale& as (perhaps surprisingly) required by the Standard. #324
  • Fixed regex_token_iterator to return correct results. #131
  • Non-member begin() and end() now take basic_string_view by value as required by the Standard. #119
  • Fixed list::splice() to work correctly when splicing exactly half of one list into another. #129
• Improved performance:
  • Fixed a codegen size regression in atomic<integral> and atomic<pointer>. #227
  • Activated x64 FrameHandler4 exception handling, reducing the size of msvcp140.dll from 588 KB to 528 KB. #154
  • Reduced the stack space consumption of list and forward_list insertion. #366
  • Improved the performance of 64-bit atomic loads on x86. #87
• Improved throughput:
  • Used if constexpr instead of tag dispatch in <any>. #173
• Enhanced behavior:
  • Improved the error message for function<Ret (Args) noexcept>. #350
  • any now supports over-aligned types. #173
  • Improved the messages that are emitted when including newer headers in older Standard modes. #252
  • Strengthened noexcept for exchange(). #364
  • std::function now avoids using typeid(void) in our _HAS_STATIC_RTTI=0 mode, for compatibility with Clang's -fno-rtti mode. #375
  • Added an error message explaining that the <experimental/coroutine>, <experimental/generator>, and <experimental/resumable> headers aren't supported with Clang. #136
• Code cleanups:
  • Removed unnecessary public keywords in struct inheritance. #219
  • Used iter[idx] for clarity in <algorithm>. #289 (Note that this was reverted in VS 2019 16.6 by #464.)
  • Fixed typos in comments and error messages. #96
  • Marked more virtual member functions as override. #302
  • Fused files together. #220 #374
  • Consistently used the modern int = 0 SFINAE technique. #226 #244 #328
  • Removed compiler bug workarounds. #175 #301 #372
  • Various cleanups (described in detail in the PRs, not repeated here). #168 #221 #269 #320 #373
• Improved documentation:
  • Added a comment explaining part of invoke()'s implementation. #368
• Infrastructure improvements:
  • Added clang-format validation. #132 #163 #255
  • Added more code format validation. #229
  • Updated dependencies. #167 #205 #231
    • Updated build compiler to VS 2019 16.4 Preview 2 (now required).
    • Updated Clang to 9.0.0 (now required).
• Updated _MSVC_STL_UPDATE. #253 #358