Resolve compiler warnings (#302)

* build: replace class noncopyable by C++11 deleted function declaration

C++11 is mandatory since commit v0.9.2-48-g8564b2f8, therefore we can
exercise the =delete keyword in class declarations to prohibit
copying.

* build: resolve -Woverloaded-virtual warnings

context.hpp:109:26: warning: "virtual vmime::context&
vmime::context::operator=(const vmime::context&)’ was hidden
[-Woverloaded-virtual=]
  109 |         virtual context& operator=(const context& ctx);
      |                          ^~~~~~~~
generationContext.hpp:153:28: note:   by ‘vmime::generationContext&
vmime::generationContext::operator=(const vmime::generationContext&)’
  153 |         generationContext& operator=(const generationContext& ctx);
      |                            ^~~~~~~~

AFAICS, there is no point in having "virtual" on an assignment operator.
Any derived classes' operator= has different signature anyway.
It is also the only class with a virtual operator=, so that's an indicator
for oddness as well.

* build: resolve -Wdeprecated-declarations warnings

encoding.cpp: In static member function "static const vmime::encoding
vmime::encoding::decideImpl(std::__cxx11::basic_string<char>::const_iterator,
std::__cxx11::basic_string<char>::const_iterator)":

encoding.cpp:161:29: warning: "std::binder2nd<_Operation>
std::bind2nd(const _Operation&, const _Tp&) [with _Operation =
less<unsigned char>; _Tp = int]" is deprecated: use "std::bind" instead
[-Wdeprecated-declarations]
  161 |                 std::bind2nd(std::less<unsigned char>(), 127)
      |                 ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

C++11 is mandatory, so just use a lambda already.

src/vmime/base.hpp

@@ -232,23 +232,6 @@ namespace vmime {
 
 		return const_pointer_cast <X, Y>(obj);
 	}
-
-	/** Inherit from this class to indicate the subclass is not copyable,
-	  * ie. you want to prohibit copy construction and copy assignment.
-	  */
-	class VMIME_EXPORT noncopyable {
-
-	protected:
-
-		noncopyable() { }
-		virtual ~noncopyable() { }
-
-	private:
-
-		noncopyable(const noncopyable&);
-		void operator=(const noncopyable&);
-	};
-
 } // vmime
 
 

src/vmime/context.hpp

@@ -106,7 +106,7 @@ protected:
 	context();
 	context(const context& ctx);
 
-	virtual context& operator=(const context& ctx);
+	context& operator=(const context& ctx);
 	void copyFrom(const context& ctx);
 
 	bool m_internationalizedEmail;

src/vmime/encoding.cpp

@@ -157,9 +157,7 @@ const encoding encoding::decideImpl(
 
 	const string::difference_type length = end - begin;
 	const string::difference_type count = std::count_if(
-		begin, end,
-		std::bind2nd(std::less<unsigned char>(), 127)
-	);
+		begin, end, [](unsigned char x) { return x < 127; });
 
 	// All is in 7-bit US-ASCII --> 7-bit (or Quoted-Printable...)
 	if (length == count) {

src/vmime/utility/stream.hpp

@@ -38,9 +38,12 @@ namespace utility {
 
 /** Base class for input/output stream.
   */
-class VMIME_EXPORT stream : public object, private noncopyable {
-
+class VMIME_EXPORT stream : public object {
 public:
+	stream() = default;
+	/* Presence of move-ctor/move-asg inhibits default copy-ctor/copy-asg */
+	stream(stream &&) = default;
+	stream &operator=(stream &&) = default;
 
 	virtual ~stream() { }