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/search/all_13.js

@@ -1,4 +1,4 @@
 var searchData=
 [
-  ['y',['y',['../structdim3.html#a83e60e072f7e8bdfde6ac05053cbb370',1,'dim3']]]
+  ['x',['x',['../structdim3.html#ac866c05f83a28dac20a153fc65b3b16c',1,'dim3']]]
 ];