Add formatting limits to the documentation page of charconv

Author: mborland

doc/modules/ROOT/pages/charconv.adoc

@@ -159,25 +159,41 @@ IMPORTANT: Same as `from_chars`, `boost::decimal::to_chars` will return a `std::
 The library offers an additional feature for sizing buffers without specified precision and in general format
 
 [#charconv_limits]
-== limits
+== Formatting Limits
 [source, c++]
 ----
 #include <boost/decimal/charconv.hpp>
 
 namespace boost {
 namespace decimal {
 
-template <typename T>
-struct limits
+template <typename DecimalType, int Precision = std::numeric_limits<DecimalType>::max_digits10>
+class formatting_limits
 {
-    static constexpr int max_chars;
-}
+public:
+
+    static constexpr std::size_t scientific_format_max_chars;
+
+    static constexpr std::size_t fixed_format_max_chars;
+
+    static constexpr std::size_t hex_format_max_chars;
+
+    static constexpr std::size_t cohort_preserving_scientific_max_chars;
+
+    static constexpr std::size_t general_format_max_chars;
+
+    static constexpr std::size_t max_chars;
+};
 
 } //namespace decimal
 } //namespace boost
 ----
 
-The member can then be used to size buffers such as:
+This class allows you to size buffers for `to_chars` without have to arbitrarily guess what size you need it to be.
+The `Precision` is defaulted to the maximum precision of the type, which is the same assumption that is made when you use `to_chars` with an unspecified precision.
+The `max_chars` variable is the largest of the 5 specified `chars_format` options.
+
+The members can then be used to size buffers such as:
 
 [source, c++]
 ----
@@ -190,7 +206,7 @@ int main()
 
     decimal32_t val {5, -1};
 
-    char buffer[limits<decimal32_t>::max_chars];
+    char buffer[formatting_limits<decimal32_t>::max_chars];
 
     auto r_to = to_chars(buffer, buffer + sizeof(buffer), val);
     *r_to.ptr = '\0';