support for YASARA PETWORLD Cif files.

[corredD]

Yasara Petworld model are written in a custom cif file, that put space in front of the catergories name.
download models from http://download.yasara.org/petworld/index.html

[BradyAJohnston]

@padix-key this is one of those examples of biotite being overly stringent when parsing that I mentioned in person last week.

[padix-key]

Thanks for the fix. I checked the CIF specification again (bottom of the document) and it seems that leading whitespaces in category names are not allowed.

DataItems ::= Tag WhiteSpace Value

However, in this case the additional strip() does increase file reading time only by approx. 3%. Hence, it would be reasonable in my opinion to support this CIF dialect.

[padix-key]

@corredD If you do not have objections, I would simply apply my suggestions and merge this PR

[corredD]

Sounds good to me @padix-key.