Add find_not() and the four find_*_backward overloads from Boost.Text. Needs

tests.

include/boost/algorithm/find_not.hpp

@@ -0,0 +1,28 @@
+/*
+   Copyright (c) T. Zachary Laine 2018.
+
+   Distributed under the Boost Software License, Version 1.0. (See accompanying
+   file LICENSE10.txt or copy at http://www.boost.org/LICENSE10.txt)
+*/
+#ifndef BOOST_ALGORITHM_FIND_NOT_HPP
+#define BOOST_ALGORITHM_FIND_NOT_HPP
+
+#include <boost/config.hpp>
+#include <utility>
+
+
+namespace boost { namespace algorithm {
+
+template<typename InputIter, typename Sentinel, typename T>        
+BOOST_CXX14_CONSTEXPR InputIter find_not(InputIter first, Sentinel last, T const & x)
+{
+    for (; first != last; ++first) {
+        if (*first != x)
+            break;
+    }
+    return first;
+}
+
+}} // namespace boost and algorithm
+
+#endif // BOOST_ALGORITHM_FIND_NOT_HPP