Improving documentation (in progress)
Build docs with make instead of directly using doxygen

This way, the README.md file is converted to doxygen acceptable
markdown first.
CL Profiler How To documentation
New GErrorF documentation
English corrections in docs
Set prototype of clu_zone_new function according to .c file definition.
Docs for CL Utils
Add table of contents to documentation.
Improve documentation (summary and introduction)
Fix (_ markdown in docs
Add missing "int" to device_query preferred vector width info
Put correct project name in license in test dir source headers
Fix segfault bugs in profiler when GError is not used.

Improved profiler code documentation.
Removed tests target from "all" target (can't be in "all" because
of stubs). Changed docs accordingly.
Improve and clarify error handling in CLUtils

Functions in CLUtils now always return CLUtils errors, not OpenCL
errors (although they wrap the latter in the error message).
CLUtils is now more in line with CLProfiler.