[bugfix] No such operator from standard: std::string += std::filesystem::path

Full Changelog: 1.6.1...1.6.2

Conceptualize bux::C_EZArgs

1. [Change] We now have 9 C_EZArgs::add_flag() overloads.
2. [Change] Must provide onParsed parameter when calling C_EZArgs::add_subcommand()
3. [Change] FUNLOG() now logs function name only (FUNCTION) instead of full function signature (FUNCSIG) to avoid logging
   convoluted long names.

EZArgs.h conceptualized

1. [Change] bux::C_EZArgs methods conceptualized.
2. [Change][Incompatible] bux::C_ErrorOrIndex knows the difference between error and help text.
3. [Change] Argument dirs of bux::search_dirs() is now typed as std::ranges::forward_range instead of in-house bux::ConstPathList
4. [Change] const std::string & is somtimes more efficient than std::string_view
5. [Change] Methods of bux::C_EZArgs tuned for uint tests to pass. But the changes are also healthier and more tolerable in the long run.
6. [New] RAW_LOGIC_ERROR(), RAW_RUNTIME_ERROR() with no source trace, just the formatted message.

p.s. This release id not for clang, which is lack of C++20 P0634R3 feature.

bux::C_ParaLog is ready for use

1. [New] bux::C_ParaLog is ready for a variety of parallel logging configurations, filtered or unfiltered.
2. [New] Necessary helper classes for implementation s.t logger users no longer need to declare child source instances explicitly.
3. [New] Add methods to ParaLog.h & SyncLog.h to support testability.
4. [New] Add unit test cases to ParaLog.h & SyncLog.h (test_paralog & test_logger)
5. [New] Update what are found in test/ to test/archlinux/aur_poc/
6. [Bug] std::uniform_int_distribution<unsigned char> no longer allowed.
7. [Change] CUR_FUNC_ for Windows (MSVC)
8. [Change] tbb is no longer implicitly needed by C++ standard library.
9. [Change] smoke_filtlog.cpp verifies 2-level log filters ok.

SCOPELOG() indentation & new macro LOG_RAW()

1. [Bug] Boudary lines of SCOPELOG() & SCOPELOGX(), and so FUNLOG & FUNLOGX(), are indented deeper in the same depth with scoped log lines.
2. [New] LOG_RAW() simply logs what is formatted by arguments between ( ) without the ordinary timestamp-tid-loglevel prefix.

bux is now cmake-installable

1. [New] Add install() derectives to enable installation thru either make install or cmake --install
2. [Bug] Add missing tbb library to both test_atomix & Dockerfile
3. [Change] Update mirrorlist links in Dockerfile

Replace include guards with #pragma once

1. Replace include guards with #pragma once
2. Sync test/archlinux/aur_poc/ with test/

Conceptualize headers & add test cases

1. 🆕 ParaUtil.h with bux::C_NumIter<>
2. 🆕 test/test_PO.cpp for PartialOrdering.h
3. 🆕 test/test_atomix.cpp for AtomiX.h
4. ✍️ Conceptualize Intervals.h PartialOrdering.h FA.h and eliminate their dependencey to <functional>
5. ✍️ Refine function handler bux::FH_ReadChar in UnicodeCvt.h to return std::optional<char> insteal of bool
6. 🚮 Remove aged function classes bux::FC_Parse* from StrUtil.h

Warning-free clang build

1. ✍️ Subdir test/ is excluded from build by default. To include test/, configure cmake with -DBUILD_TEST=1
2. ✍️ bux::C_EzArgs::parse() accepts argc parameter both in type size_t or int
3. ✍️ Intervals.h rehauled to use C++20 concepts to smartly reduce lines and eliminate clang warnings altogether.
4. ✍️ Eliminate clang warnings here & there.
5. 🆕 test/hrtn to demangle external symbols freely.

Backward incompactible release due to function prototype changes

1. ✍️ Use FMT_STRING() everywhere.
2. ✍️ Change a few function argument types from const std::string & to std::string_view. This will break parsergen prior to v1.6.2