Update docs:

- Some comments in hip_hcc.cpp
 - document hipHostRegister* flags.
 - expand docs on hipHostRegister/Unregister. Use "register" rather than
   "pin" to describe action these take.
 - change required CUDA version to 6 (require unified memory)
 - remake doxygen.

docs/RuntimeAPI/html/group__API.html

@@ -110,7 +110,7 @@ Modules</h2></td></tr>
 </div><!-- contents -->
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 <hr class="footer"/><address class="footer"><small>
-Generated on Thu Feb 18 2016 20:42:16 for HIP: Heterogenous-computing Interface for Portability by &#160;<a href="http://www.doxygen.org/index.html">
+Generated on Wed Mar 23 2016 23:11:07 for HIP: Heterogenous-computing Interface for Portability by &#160;<a href="http://www.doxygen.org/index.html">
 <img class="footer" src="doxygen.png" alt="doxygen"/>
 </a> 1.8.6
 </small></address>