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/streams/OutputStream.cpp

@@ -21,6 +21,8 @@
 */
 //==============================================================================
 
+#include <algorithm>
+
 namespace beast
 {
 
@@ -98,7 +100,8 @@ bool OutputStream::writeShortBigEndian (short value)
 
 bool OutputStream::writeInt32 (std::int32_t value)
 {
-    static_bassert (sizeof (std::int32_t) == 4);
+    static_assert (sizeof (std::int32_t) == 4,
+        "The size of an integer must be exactly 4 bytes.");
 
     const unsigned int v = ByteOrder::swapIfBigEndian ((std::uint32_t) value);
     return write (&v, 4);
@@ -106,7 +109,8 @@ bool OutputStream::writeInt32 (std::int32_t value)
 
 bool OutputStream::writeInt (int value)
 {
-    static_bassert (sizeof (int) == 4);
+    static_assert (sizeof (int) == 4,
+        "The size of an integer must be exactly 4 bytes.");
 
     const unsigned int v = ByteOrder::swapIfBigEndian ((unsigned int) value);
     return write (&v, 4);
@@ -114,14 +118,16 @@ bool OutputStream::writeInt (int value)
 
 bool OutputStream::writeInt32BigEndian (int value)
 {
-    static_bassert (sizeof (std::int32_t) == 4);
+    static_assert (sizeof (std::int32_t) == 4,
+        "The size of an integer must be exactly 4 bytes.");
     const std::uint32_t v = ByteOrder::swapIfLittleEndian ((std::uint32_t) value);
     return write (&v, 4);
 }
 
 bool OutputStream::writeIntBigEndian (int value)
 {
-    static_bassert (sizeof (int) == 4);
+    static_assert (sizeof (int) == 4,
+        "The size of an integer must be exactly 4 bytes.");
     const unsigned int v = ByteOrder::swapIfLittleEndian ((unsigned int) value);
     return write (&v, 4);
 }
@@ -274,7 +280,7 @@ int OutputStream::writeFromInputStream (InputStream& source, std::int64_t numByt
     while (numBytesToWrite > 0)
     {
         char buffer [8192];
-        const int num = source.read (buffer, (int) bmin (numBytesToWrite, (std::int64_t) sizeof (buffer)));
+        const int num = source.read (buffer, (int) std::min (numBytesToWrite, (std::int64_t) sizeof (buffer)));
 
         if (num <= 0)
             break;