Autotune: increase stack size and step size

The stack size is borderline too low after going to gcc 4.8. The
step size of 0.35 instead of 0.25 makes it produce better values
for all the microquads that are popping up.
Autotune: update copyright header
Merge pull request #1117 from peabody124/autotune_stack

Autotune: increase stack size and step size