Merge branch 'develop'

Merge branch 'develop'

Merge branch 'develop'

Merge branch 'develop'

Merge branch 'develop'

Fix standalone endianness macros. (boostorg#678)

* Fix comment typos: "endinaness" to "endianness"
* Change the C++20 checks (for both `__cplusplus` and `_MSVC_LANG`)
  to be strict: `> 202000L` to `>= 202002L`
* Add an `#error` when C++20 `<bit>` is missing, just in case.
* Fix the `_WIN32` definitions. All Windows platforms are little-endian
  (regardless of x86/x64/ARM/ARM64), `<boost/predef/other/endian.h>`
  correctly reports little-endian, and MSVC's STL simply hardcodes
  `enum class endian { little = 0, big = 1, native = little };`, see
  https://github.com/microsoft/STL/blob/f75c7f596c7b491168fefb5eff5164ab7ae36867/stl/inc/bit#L271 .
* Add a `static_assert` to verify that exactly one of
  `BOOST_MATH_ENDIAN_BIG_BYTE` or `BOOST_MATH_ENDIAN_LITTLE_BYTE` is
  true. This avoids the need for "Endian type could not be identified"
  consistency checks below.
* Fix boostorg#677 by not testing `BOOST_MATH_ENDIAN_BIG_BYTE` and
  `BOOST_MATH_ENDIAN_LITTLE_BYTE` with the preprocessor, as
  `std::endian::native` isn't a preprocessor constant. Now, this simply
  expects `BOOST_MATH_ENDIAN_BIG_BYTE` to be usable in a constant
  expression, and assumes (due to the consistency check above)
  that if we aren't big-endian, we must be little-endian.

Fix duplicate typedef in mp.hpp

Merge branch 'develop'

Fixed Conflicts:
	include/boost/math/special_functions/log1p.hpp

Minimax and distribution_explorer to examples. (boostorg#620)

* Minimax and distribution_explorer to examples.

* Move minimax to tools.

Merge pull request boostorg#593 from boostorg/fix_gini_coef

Fix gini coefficient calculation.