Remove use of auto in introductory examples

doc/charconv/overview.adoc

@@ -21,13 +21,13 @@ This library requires a minimum of C++11.
 
 const char* buffer = "42";
 int v = 0;
-auto r = boost::charconv::from_chars(buffer, buffer + std::strlen(buffer), v);
+boost::charconv::from_chars_result r = boost::charconv::from_chars(buffer, buffer + std::strlen(buffer), v);
 assert(r.ec == std::errc());
 assert(v == 42);
 
 char buffer[64];
 int v = 123456;
-auto r = boost::charconv::to_chars(buffer, buffer + sizeof(buffer) - 1, v);
+boost::charconv:to_chars_result r = boost::charconv::to_chars(buffer, buffer + sizeof(buffer) - 1, v);
 assert(r.ec == std::errc());
 assert(!strncmp(buffer, "123456", 6)); // Strncmp returns 0 on match
 
@@ -46,4 +46,4 @@ Tested on https://github.com/cppalliance/charconv/actions[Github Actions] and ht
 Currently only https://en.cppreference.com/w/cpp/compiler_support/17[GCC 11+ and MSVC 19.24+] support both integer and floating-point conversions in their implementation of `<charconv>`. +
 
 If you are using either of those compilers, Boost.Charconv is at least as performant as `<charconv>`, and can be up to several times faster.
-See: <<Benchmarks>>
+See: <<Benchmarks>>