Updating max payload size to new 2KB limit and adding category field in the payload.
Validate the device token length. Otherwise the frame can be sent with an incorrect length.
Fix tests after device token length check.
Merge pull request #26 from benkraus/master

Updating max payload size to new 2KB limit and adding category field
Merge pull request #27 from tstranex/master

Validate the device token length.
Merge upstream
Use bytes arrays for cert and key
Merge branch 'master' into cert-bytes