common: Rename binary_find.h to algorithm.h

Makes the header more general for other potential algorithms in the
future. While we're at it, include a missing <functional> include to
satisfy the use of std::less.

src/common/algorithm.h

@@ -0,0 +1,22 @@
+// Copyright 2019 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <algorithm>
+#include <functional>
+
+namespace Common {
+
+template <class ForwardIt, class T, class Compare = std::less<>>
+ForwardIt BinaryFind(ForwardIt first, ForwardIt last, const T& value, Compare comp = {}) {
+    // Note: BOTH type T and the type after ForwardIt is dereferenced
+    // must be implicitly convertible to BOTH Type1 and Type2, used in Compare.
+    // This is stricter than lower_bound requirement (see above)
+
+    first = std::lower_bound(first, last, value, comp);
+    return first != last && !comp(value, *first) ? first : last;
+}
+
+} // namespace Common