Increased number of friends tested in tox_test.
Added custom packet functions to public tox api.

This should make it easy for people to use toxcore to power many
types of networked applications.
This fixes an issue where nodes could stay unannounced for certain
periods of time.

Online nodes should now be able to announce themselves continuously.
Updated docs.

Fixed possible issue in last commit.
Fixed typo.
Added tests for custom lossy and lossless packets.

Fixed bug with lossless packets.
Merge branch 'master' into encrypted_data
compiling against nacl seems to break VANILLA_NACL...