No meaningful changes.

[Rework] Massive spelling fix from @jsoref

Issue: #572

Previously, upstream.get_addr function returned the new address of the
upstream. Unfortunately, it was used for printing addresses. It caused
the following situation: let's imagine we have A1 and A2 where A1 was
initially selected. So the connection was performed to A1:

                           Current addr   Selected addr

   Connect+---------+      A2+------>A1   A1
                    |
+-+Print failure<---+      A1+------>A2   A2
|                        +----+
+->Mark failure+-------->+ A2 |
                         +----+

But the failure OP as well as log message told about `A2` where the real
problem happened with `A1`.

This commit adds distinguishing between getting the next and the current
address of the upstream resolving this issue.

- Select ipv4/unix addresses if they exist and use ipv6 for ipv6 only
  upstreams (since the support of ipv6 is poor in many OSes and
  environments).
- Free IP list on upstream destruction.
- Add test cases for addresses selection.
- Allow adding of free form IP addresses to upstreams.

This reverts commit e0483657ff.

Add descriptions for some rspamd API functions (no functional changes).

--HG--
rename : linux/rspamd => linux/rspamd_debian.in

* Add ability to select between round-robin and master-slave algorithms for dns servers

Now all comments in commit logs beginning with '*' would be included in changelog, so
important changes would be separated from small ones.

* Adopt build system for new structure

--HG--
rename : cfg_file.h => src/cfg_file.h
rename : cfg_file.l => src/cfg_file.l
rename : cfg_file.y => src/cfg_file.y
rename : cfg_utils.c => src/cfg_utils.c
rename : controller.c => src/controller.c
rename : filter.c => src/filter.c
rename : filter.h => src/filter.h
rename : fstring.c => src/fstring.c
rename : fstring.h => src/fstring.h
rename : main.c => src/main.c
rename : main.h => src/main.h
rename : mem_pool.c => src/mem_pool.c
rename : mem_pool.h => src/mem_pool.h
rename : memcached-test.c => src/memcached-test.c
rename : memcached.c => src/memcached.c
rename : memcached.h => src/memcached.h
rename : perl.c => src/perl.c
rename : perl.h => src/perl.h
rename : plugins/regexp.c => src/plugins/regexp.c
rename : plugins/surbl.c => src/plugins/surbl.c
rename : protocol.c => src/protocol.c
rename : protocol.h => src/protocol.h
rename : upstream.c => src/upstream.c
rename : upstream.h => src/upstream.h
rename : url.c => src/url.c
rename : url.h => src/url.h
rename : util.c => src/util.c
rename : util.h => src/util.h
rename : worker.c => src/worker.c