Simplify imports

Signed-off-by: Michal Čihař <michal@cihar.com>
Use CDLL for loading dll, it is cleaner than using getattr

Signed-off-by: Michal Čihař <michal@cihar.com>
Separate list of possible library names

Signed-off-by: Michal Čihař <michal@cihar.com>
Move library loading and initialization to the class

There is no need to have this in separate code block, it really belongs
to the class constructor.

Signed-off-by: Michal Čihař <michal@cihar.com>
Document library names

Signed-off-by: Michal Čihař <michal@cihar.com>