Fix various links such as Travis CI build badge and cargo repository
link.
The use of try! macro is deprecated in favor of ?. Occurences were
replaced.
The functions default_scale() and default_one() were never used, they were
deleted.
Use of Error::description is deprecated in favor of Display or
to_string. Implementation of Error::description was deleted, as
impl Display for UrdfError already existed.
Used std::fs::read_to_string instead of custom implementation
try!macro is deprecated in favor of?. Occurences were replaced.default_scale()anddefault_one()were never used, they were deleted.Error::descriptionis deprecated in favor ofDisplayorto_string. Implementation ofError::descriptionwas deleted, asimpl Display for UrdfErroralready existed.std::fs::read_to_stringinstead of custom implementation