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

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

test/test_rewind.cxx

@@ -32,7 +32,7 @@ public:
 	}
 
 	/* virtual methods from InputStream */
-	bool IsEOF() override {
+	bool IsEOF() noexcept override {
 		return remaining == 0;
 	}