*: add "noexcept" to many, many function prototypes

This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

src/MusicBuffer.hxx

@@ -41,7 +41,7 @@ public:
 	 * @param num_chunks the number of #MusicChunk reserved in
 	 * this buffer
 	 */
-	MusicBuffer(unsigned num_chunks);
+	MusicBuffer(unsigned num_chunks) noexcept;
 
 #ifndef NDEBUG
 	/**
@@ -71,13 +71,13 @@ public:
 	 * @return an empty chunk or nullptr if there are no chunks
 	 * available
 	 */
-	MusicChunk *Allocate();
+	MusicChunk *Allocate() noexcept;
 
 	/**
 	 * Returns a chunk to the buffer.  It can be reused by
 	 * Allocate() then.
 	 */
-	void Return(MusicChunk *chunk);
+	void Return(MusicChunk *chunk) noexcept;
 };
 
 #endif