Release 0.8.0

Release 0.8.0

* New fuzzy check logic:
	- use shingles algorithm for fuzzy matching
	- use blake2 instead of md5 for larger output space
	- combine fuzzy and strict matching
	- allow to organize private storages by means of keys
	- preserve compatibility with previous versions
* New fuzzy storage:
	- use sqlite instead of own memory based hash tables
	- rework commands interface
	- add conversion from the old format
	- add fuzzy match by shignles
	- support old rspamd versions
* Add lemmatizing for words used in fuzzy hashes that allows to improve match
quality by using of the first forms of all words
* Rework language detection
* Fix several critical bugs, memory leaks and deadlocks:
	- memory leak in HTML nodes parsing
	- deadlock in logger code
	- deadlock in signals processing
	- crashes in fuzzy_storage
	- crashes in tokenizers if the input was empty
* Import new libucl with several bugfixes and improvements
* Support listening on ipv6 addresses only
* Fix macro expansion in SPF module
* Several bugfixes in DKIM module
* Add load headers support for mime parts to the lua API
* Add documentation for:
	- workers in general
	- fuzzy_storage worker
	- fuzzy_check plugin
	- mimepart and textpart lua API modules

Signed-off-by: Vsevolod Stakhov <vsevolod@highsecure.ru>