Update contributing.md with C++11

CONTRIBUTING.md

@@ -1,7 +1,7 @@
Code Stuff
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 * We use C++03 with some C++11 extensions (ask if you think that something would be useful)
 * We use the subset of C++11 supported by MSVC 2013 (ask if you think that something would be useful)
 * Use the provided wrappers for OS stuff:
  - Threading is done by inheriting from `cIsThread`, thread synchronization through `cCriticalSection`, `cSemaphore` and `cEvent`, file access and filesystem operations through the `cFile` class, high-precision timers through `cTimer`, high-precision sleep through `cSleep`
 * No magic numbers, use named constants: