split to multiple functions

caused by indirect testing of tokenize function

* renamed from sockaddr_to_string
* improved variables naming
* return -1 to be ssame as other utilities
* make sockaddr pointer constant
* assert check of input pointers

* add assert check
* data with zero len are invalid

- renamed from concat_msg
- return result string size
- NULL check of arguments
- check of malloc

We are going to hardly ever modify received data and if so
it is better to discard const at this pointa rather than at any
tokenization.

First welcome message is sent before any data.
Messages are now sent one by one and not in batches.

* send welcome message first - so proxy can identify Minipots
* removed messages buffering - messages are sent separately and not in
  batches in regular intervals
* added send and linger timeouts - so Minipots doesn't hang when
output ZMQ queue is full and more sends are possible. This happens when
there is no PULL peer receibeing the messages running.

We can check for gperf unconditionally. No idea why would existence of a
file prevent us for checking for iperf, but this particular check fails
when cross-compiling. And dropping it shouldn't hurt.

checking for ./bootstrap... configure: error: cannot check for file existence when cross compiling

Added
* Gitlab CI
* libevent_logc and libczmq_logc as dependency

Changed
* Repository layout
* Minimal version of LogC to 0.2.0
* SMTP minipot: split received username string to username and domain
* integration tests: check timestamp value

Fixed
* Out of source tree build