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.


[ROCm/hip commit: eced013ae4]

projects/hip/docs/RuntimeAPI/html/search/all_3.js

@@ -1,5 +1,6 @@
 var searchData=
 [
+  ['canmaphostmemory',['canMapHostMemory',['../structhipDeviceProp__t.html#ac2143f5448607d1a02a9e8783fcf06a1',1,'hipDeviceProp_t']]],
   ['clockinstructionrate',['clockInstructionRate',['../structhipDeviceProp__t.html#a6fbf3b08a1a08ae700f1a06265f6666b',1,'hipDeviceProp_t']]],
   ['clockrate',['clockRate',['../structhipDeviceProp__t.html#a1dd15bee43692b8649dfbdc1adbaaf96',1,'hipDeviceProp_t']]],
   ['computemode',['computeMode',['../structhipDeviceProp__t.html#ae7d9216f8583a703359d0b9373823f5d',1,'hipDeviceProp_t']]],