Add parallel algorithms (#39)

* Add parallel algorithms

CPP17.md

@@ -28,6 +28,7 @@ C++17 includes the following new library features:
 - [std::filesystem](#stdfilesystem)
 - [std::byte](#stdbyte)
 - [splicing for maps and sets](#splicing-for-maps-and-sets)
+- [parallel algorithms](#parallel-algorithms)
 
 ## C++17 Language Features
 
@@ -394,6 +395,17 @@ m.insert(std::move(e));
 // m == { { 1, "one" }, { 3, "three" }, { 4, "two" } }
 ```
 
+### Parallel algorithms
+Many of the STL algorithms, such as the `copy`, `find` and `sort` methods, started to support the *parallel execution policies*: `seq`, `par` and `par_unseq` which translate to "sequentially", "parallel" and "parallel unsequenced".
+
+```c++
+std::vector<int> longVector;
+// Find element using parallel execution policy
+auto result1 = std::find(std::execution::par, std::begin(longVector), std::end(longVector), 2);
+// Sort elements using sequential execution policy
+auto result2 = std::sort(std::execution::seq, std::begin(longVector), std::end(longVector));
+```
+
 ## Acknowledgements
 * [cppreference](http://en.cppreference.com/w/cpp) - especially useful for finding examples and documentation of new library features.
 * [C++ Rvalue References Explained](http://thbecker.net/articles/rvalue_references/section_01.html) - a great introduction I used to understand rvalue references, perfect forwarding, and move semantics.