Hotfix v1.0.1: fast hotfixes before the exam

Release v1.0.0: improvements and fix for the exam

The function send sends an integer with number of bytes sent.
The function recv expects that number as first 4-byte data.

The Robin Client now is more interactive with the user.

Fix all differences with the project requirements.

Release v0.8.0: add Robin API and Robin Client CLI

Release v0.7.1: Save users on filesystem

Hash passwords when received from clients.

Release v0.7.0: Followers and Robin Cips

Release v0.6.2: minor bug fixes and improvements

Release v0.6.1: use pthread_cancel safe funcs

lib/alloc_safe.h contains static inline functions to allocate and free
pointers in a safe way to correctly clean-up the resources on SIGINT.

In these way there aren't spurious memory leaks found by Valgrind during
debug of new code.

Release v0.6.0: add follow RC and correct cleanup

Users can follow each others and list its followings.

Correct cleaning-up on SIGINT has been add to debug correctly
with Valgrind. All resources are freed on SIGINT.

Release 0.5.0: add Robin User and Robin Connection

Robin User layer is used to handle access to user data between connections.
Robin Manager has been merged into Robin Connection layer.

Release v0.4.1: several fixes and improvements