fix pacakge import

Postgres driver has moved to github.com/lib/pq
improve checking for sane characters

* \r is also a posix escape
* html may start with '</ ...>' not only with '<...'
check maintainer_link also for sane link specifiers
add more unit tests
add more unit tests

rename one file to check for two OGD metadata fields
Every aspect of the OGD Check is now unit tested
add test to check the urls as well

* does the dataset actually exist?
* go fmt the source