Select device by device or platform name

Refactor device selection, with generic function now having its
own typedef definition.
Example 'matmult' uses device selection via device or platform name

Fix some bugs on device selection via device or platform name in
clutils.c and clutils.h
Add device vendor to device_query.c
Improved Makefile comments for configuring OpenCL headers and libs
Documentation update
Add device selection by vendor

Refactored device selection via device information, and consequently
kernel_info.c had to be modified also.
Example matmult conforms with refactored device selection via info

Example matmult allows to chose device via vendor info