Print name of task that forgot to implement method
Add buffer views for larger-than-GPU data

This change adds ufo_buffer_get_array_view() which returns partial data as an
OpenCL cl_mem object which must be freed by the client. It is intended to work
with data that is presumably larger than a GPU could hold.
Merge pull request #24 from ufo-kit/add-views

Add views
Add group scheduler with different policy
Fix execution for reductors
Fix alignment
Fix segfault
Fix scheduling and add profiling