Added facility to apply a filter function to captured output.

[kevinmcguinness]

Adds a facility to apply a filter function to captured output. This is useful in situations where your experiment code uses a console based progress bar or similar in the text UI, but you would rather not have the observer store the control characters like backspaces and linefeeds in the database. This can be achieved by setting the captured_out_filter on the run or experiment as follows:

from sacred.utils import apply_backspaces_and_linefeeds

ex = Experiment('progress')
ex.captured_out_filter = apply_backspaces_and_linefeeds

It would be possible to also implement this kind of thing by subclassing the observers and filtering the text there, or by changing the observers directly. However, in this case, the user would need to configure all observers. It would also make it harder to implement adding the observer via the command line interface like you can do now.

[coveralls]

Coverage increased (+0.3%) to 90.997% when pulling 4f3cca7 on kevinmcguinness:feature/captured-out-filter into 9446a76 on IDSIA:master.

[Qwlouse]

Hey Kevin,
what a nice PR. You even added an example. Thanks a lot!
I was thinking about adding this feature myself, but I hesitated because I was concerned with the speed of the filter. But by making it optional and configurable this is not much of a problem. And maybe we can someday add a C-extension to do it fast.

I'm merging it now, but it'll need some work for the new 0.7 release since I'm trying to switch to file-descriptor based capturing.

[black-puppydog]

@Qwlouse: would the new capturing be able to catch printf() and/or cout << from C/C++ extensions?

[Qwlouse]

For the 0.7 release I've tried to switch to a file-descriptor based capturing that would also catch printf and such. Right now, it doesn't yet work smoothly on windows. But I intend on fixing that problem soon. So from the next release on, all outputs to stdout, even from C extensions should be captured, yes.

[black-puppydog]

Clever /me just found the 0.7 branch and will play around with that a bit :P

Any chance you have a feature branch lying around somewhere? I'm on Linux exclusively anyway, and have a lot of cout happening. I can work around that for now with the logging mechanism of our cluster here, but collecting everything in sacred would be much preferred :)