Add release notes for: Charconv, Math, Multiprecision, Random (#622)

* Add charconv release notes

* Add math release notes

* Add test release notes

* Add random release notes

* Improve wording based on review feedback

Author: mborland

release-notes/boost_1_91_0.adoc

@@ -66,6 +66,9 @@ boost_at:/doc/libs/1_91_0/[Documentation]
 ** Removed dependency on Boost.StaticAssert.
 ** Added `HTTP2-Settings` to HTTP field enum.
 
+* boost_phrase:library[Charconv,/libs/charconv/]:
+** Fixed overflow in `to_chars` of negative 128-bit integers whose absolute value is less than 2^64
+
 * boost_phrase:library[Core,/libs/core/]:
 ** The header `boost/is_placeholder.hpp` has been moved from Bind to Core. (https://github.com/boostorg/core/issues/90[#90])
 
@@ -110,6 +113,18 @@ boost_at:/doc/libs/1_91_0/[Documentation]
 * boost_phrase:library[Log,/libs/log/]:
 ** Enabled building interprocess communication support on Cygwin by default.
 
+* boost_phrase:library[Math,/libs/math/]:
+** Added `find_non_centrality` finding function for `non_central_f_distribution`
+** Added parameter finding function for `non_central_t_distribution`
+** Added function for the log of the incomplete gamma function, `lgamma_q`
+** Added function for the log of the lower incomplete gamma function, `lgamma_p`
+** Added `domain()` function for `pchip`
+** Fixed broken CUDA support in the logistic distribution
+** Fixed incorrect floating point traits for Windows on ARM64
+** Fixed incorrect result `ibeta` for large arguments
+** Fixed incorrect `ellint_2` for N * PI / 2 for phi argument.
+** Require user to explicitly enable CUDA rather than assuming based off presence of NVCC
+
 * boost_phrase:library[MultiIndex,/libs/multi_index/]:
 ** *Breaking change:* All type lists accepted or provided by the library (`indexed_by`,
 `tag`, nested typedefs `index_specifier_type_list`, `index_type_list`, `iterator_type_list`
@@ -203,6 +218,9 @@ This addresses issues https://github.com/boostorg/optional/issues/132[#132] and
    macro to `1` to enable.
 ** `boost::pfr::for_each_field*()` functions now work well with stateful visitors.
 
+* boost_phrase:library[Random,/libs/random/]:
+** Fixed unsigned types in `binomial_distribution` being inadvertently unsupported.
+
 * boost_phrase:library[Redis,/libs/redis/]:
 ** Added built-in support for **Sentinel** deployments, which can be configured
    using `config::sentinel`. The library handles master/replica discovery,
@@ -265,6 +283,9 @@ This addresses issues https://github.com/boostorg/optional/issues/132[#132] and
    instead of having that as a precondition. The old behavior is now spelled `unsafe_value()`.
 ** Added `boost/system/unwrap_and_invoke.hpp`.
 
+* boost_phrase:library[Test,/libs/test/]:
+** Add friend operators for proper comparisons of `std::optional` with GCC < 10
+
 * boost_phrase:library[TypeIndex,/libs/type_index/]:
 ** Optimized CTTI type comparisons starting from C++20.
 ** `ctti_type_index::name()` now returns pretty value by default in C\+\+14 and more modern C\+\+ standards.