raw_istream and kin: a few cleanups.

anchor() doesn't seem to change compiler output in current compilers, so
remove it.  Use default where appropriate rather than empty bodies.

src/raw_istream.cpp

@@ -11,8 +11,6 @@
 
 using namespace nt;
 
-void raw_istream::anchor() {}
-
 bool raw_mem_istream::read(void* data, std::size_t len) {
   if (len > m_left) return false;
   std::memcpy(data, m_cur, len);

src/raw_istream.h

@@ -13,11 +13,9 @@
 namespace nt {
 
 class raw_istream {
-  void anchor();
-
  public:
-  raw_istream() {}
-  virtual ~raw_istream() {}
+  raw_istream() = default;
+  virtual ~raw_istream() = default;
   virtual bool read(void* data, std::size_t len) = 0;
   virtual void close() = 0;
 
@@ -28,7 +26,7 @@ class raw_istream {
 class raw_mem_istream : public raw_istream {
  public:
   raw_mem_istream(const char* mem, std::size_t len) : m_cur(mem), m_left(len) {}
-  virtual ~raw_mem_istream() {}
+  virtual ~raw_mem_istream() = default;
   virtual bool read(void* data, std::size_t len);
   virtual void close() {}
 

src/raw_socket_istream.cpp

@@ -9,8 +9,6 @@
 
 using namespace nt;
 
-raw_socket_istream::~raw_socket_istream() {}
-
 bool raw_socket_istream::read(void* data, std::size_t len) {
   char* cdata = static_cast<char*>(data);
   std::size_t pos = 0;

src/raw_socket_istream.h

@@ -18,7 +18,7 @@ class raw_socket_istream : public raw_istream {
  public:
   raw_socket_istream(NetworkStream& stream, int timeout = 0)
       : m_stream(stream), m_timeout(timeout) {}
-  virtual ~raw_socket_istream();
+  virtual ~raw_socket_istream() = default;
   virtual bool read(void* data, std::size_t len);
   virtual void close();