Merge pull request #34 from syockit/syukri

Add OVF1 binary 8 read support and test cases for OVF1/2
datatable: flush every 5 seconds
re-add testdata/mask.png
start cmd/mumax3-fft
mumax3-fft: zero-padding
mumax3-fft windowing
mumax3-fft doc
mumax3-fft docs
typo fix
mumax3-fft cleanup
mumax3-fft cleanup
mumax3-fft interpolation
interpolate cleanup
typo fix
mumax3-fft cleanup
work around gui crash by relax with temperature
mumax3-fft: fix crash on negative times
stash
document -divcol
-divcol doc