Merge pull request #23 from ufo-kit/simplify-tasks

[WIP] Simplify task interface
Dynamically allocate build log memory
Fix error handling for wrong kernels
Fix update buffer size
Merge pull request #25 from ufo-kit/update-buffer-resize

Fix update buffer size
Return from ufo_buffer_resize if size is the same
Fix event tracing and improve API a bit
Add group scheduler with different policy
Fix execution for reductors
Fix alignment
Fix segfault