Miscellaneous: Add mio (fix #688)

README.md

@@ -815,6 +815,7 @@ A curated list of awesome C++ (or C) frameworks, libraries, resources, and shiny
 * [libusb](https://libusb.info/) - A universal USB library which allows for portable access to USB devices. [LGPL2]
 * [Mach7](https://github.com/solodon4/Mach7) - A Pattern-matching library for C++. [BSD]
 * [meta](https://github.com/skypjack/meta) - Header-only, non-intrusive and macro-free runtime reflection system in C++. [MIT]
+* [mio](https://github.com/mandreyel/mio) - Cross-platform C++11 header-only library for memory mapped file IO. [MIT]
 * [PEGTL](https://github.com/ColinH/PEGTL) - The Parsing Expression Grammar Template Library, a C++11 parser library. [MIT]
 * [PHP-CPP](https://github.com/CopernicaMarketingSoftware/PHP-CPP) - A library to build PHP extensions with C++. [Apache2] [website](http://www.php-cpp.com/)
 * [Remote Call Framework](http://www.deltavsoft.com/) - Inter-process communication framework for C++. [GPL2/Commercial]