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__HIP-ENV.html

@@ -101,7 +101,7 @@ int&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="group
 </div><!-- contents -->
 <!-- start footer part -->
 <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>