Reduce Beast public interface and eliminate unused code:

Beast includes a lot of code for encapsulating cross-platform differences
which are not used or needed by rippled. Additionally, a lot of that code
implements functionality that is available from the standard library.

This moves away from custom implementations of features that the standard
library provides and reduces the number of platform-specific interfaces
andfeatures that Beast makes available.

Highlights include:
* Use std:: instead of beast implementations when possible
* Reduce the use of beast::String in public interfaces
* Remove Windows-specific COM and Registry code
* Reduce the public interface of beast::File
* Reduce the public interface of beast::SystemStats
* Remove unused sysctl/getsysinfo functions
* Remove beast::Logger

beast/module/core/text/StringArray.cpp

@@ -21,6 +21,8 @@
 */
 //==============================================================================
 
+#include <algorithm>
+
 namespace beast
 {
 
@@ -321,7 +323,7 @@ void StringArray::move (const int currentIndex, int newIndex) noexcept
 String StringArray::joinIntoString (const String& separator, int start, int numberToJoin) const
 {
     const int last = (numberToJoin < 0) ? size()
-                                        : bmin (size(), start + numberToJoin);
+                                        : std::min (size(), start + numberToJoin);
 
     if (start < 0)
         start = 0;