BUG : changed logic on converting to scalar

Instead of checking on size == 1 check on ndim == 0.  This
matters for `tt.sum()` (should covert to scalar) vs
`tt.sum(keepdims=True)` (should not convert to scalar).
TST : added tests of to-scalar casting
Merge pull request #50 from tacaswell/frame_tweak

BUG : changed logic on converting to scalar
If C compiling fails, restart setup without extensions.
Merge pull request #51 from danielballan/graceful-decay

If C compiling fails, restart setup without extensions.
FIX: Hotfix merge mistake.
Merge pull request #53 from danielballan/hotfix

FIX: Hotfix merge mistake.
ENH: Add nice repr for all classes.
Merge pull request #54 from danielballan/restore-repr

ENH: Add nice repr for all classes.
FIX: Frame from Video() should have frame_no.
ENH: Add boolean kwarg 'use_cache' to Video, useful for testing.
TST/CLN: Test that all classes have frame_no attr and that it is correct.
TST: Test that all classes accept a process_func.
FIX/CLN: Common process_func validation for all classes. Add it where missing.

FIX: Untested tifffile code returns Frame, too.
TST: Test two process_func examples on each class. Verify positional arg.
Merge pull request #52 from danielballan/fix-oversights

Fix oversights
ENH: Add as_grey option and update docstrings.
Merge pull request #58 from danielballan/as-grey

ENH: Add convenient greyscale conversion.
HOTFIX: as_grey unintentionally converts ints to floats.
Merge pull request #59 from danielballan/fix-as-grey

HOTFIX: as_grey unintentionally converts ints to floats.