Fix tac, toc, loop_timer to return float

[oyamad]

Close #386

[coveralls]

Coverage decreased (-0.0007%) to 94.908% when pulling f49bd9b on tac_toc into f0dc490 on master.

[mmcky]

@oyamad from a backwards compatibility perspective are there any changes to usage?
I don't think so as I see you've used verbose=True as a default so the floats will print.

[mmcky]

thanks @oyamad this looks good.

[oyamad]

Yes, this is backward incompatible:

Version	Output type	Print option	Output option
-0.3.6.2	float	-	-
0.3.7	str or None	print_output	output
This PR	float	verbose	-

[mmcky]

@oyamad thanks. This is mainly used as a utility so I think that is fine. I will just do a search across the repo to make sure there are no other changes.