Fix conversion tests
tesseract produces hocr files with ending .hocr not .html
Squashed commit of the following:

commit 4b53d6ef353b2398720ae3222708b3466b32fc21
Author: Benjamin Kiessling <mittagessen@l.unchti.me>
Date:   Fri Jul 4 16:45:38 2014 +0200

    Turns out compiling is not equal to functionality tests. Who would've
    thought?

commit 082e1bbfd8f990ea3d11ed9b3b42b7c304ac06cd
Author: Benjamin Kiessling <mittagessen@l.unchti.me>
Date:   Fri Jul 4 14:20:16 2014 +0200

    Actually add rgb_to_gray function to module

commit 84703449f6f07572c2ef1c7fe63b086f264d7ae2
Author: Benjamin Kiessling <mittagessen@l.unchti.me>
Date:   Mon Jun 30 15:09:40 2014 +0200

    Add rgb_to_gray wrapper

commit 547205de64435eda2d3f081a985a5fc8040b2bf4
Author: Benjamin Kiessling <mittagessen@l.unchti.me>
Date:   Mon Jun 30 14:50:46 2014 +0200

    Fix init function

commit aa9ed9d5b1ec48d57b172473272a7ccaeca91146
Author: Benjamin Kiessling <mittagessen@l.unchti.me>
Date:   Mon Jun 30 14:44:21 2014 +0200

    Update setup.py for new c extension

commit 6d0ed9ee79b44f2ab00262a10d2ba89838aa29e8
Author: Benjamin Kiessling <mittagessen@l.unchti.me>
Date:   Mon Jun 30 14:35:41 2014 +0200

    deskew is now leper and does binarization(s)
Add page-wise dewarping function
Add handlers for incorrect input color depth
Ensure correct color depth for output by making it the responsibility of
the user.
leper does more than deskewing now
Don't need python-fs any more