Changing the prefix options for reading

Signed off by: Daniel Alves <danpaulalves@gmail.com>
Overriding save and destroy methods for readings

Signed off by: Daniel Alves <danpaulalves@gmail.com>
Rescuing errors on reading and added tests

Signed off by: Daniel Alves <danpaulalves@gmail.com>
Merge pull request #15 from mezuro/fixing_reading

Fixing reading