Error argument in the connection handler is not always set and in some
cases provides meaningless values. For example, every TLS module returns
its specific error codes.
Current solution unifies error codes and allows to distinguish between
different types of disconnection.
Fixes#123.
@sjaeckel integrated clang-format with formal coding style. Run his
script and commit changes.
There are pros and cons of this commit.
Mixed coding style is a "broken window". A good single style simplifies
reading and writing code.
On the other hand, this is a big change which will lead to conflicts.
