YB.ORM-0.4.8 released

* Fix broken DomainObj::find(); Fix warnings
* Fix broken method Property::is_null(); More checks not to dereference NULL pointer
* Fix possible buffer underrun
* Sync micro_http with card-proxy
* Fix problem with removing of non existent backup file 
* #28: fixing defects found by Coverity Scan
* #26: do not throw on saving a DataObject twice;
* check if logger is present in EngineBase
* #25: fixes for msvc
* Fix resource exhaustion handling in main loop of micro_http listener.
* #25: apply aliases for generated SELECT statements
* #25: generate short mnemonic aliases for tables
* Move the interlocked connection opening logic from drivers to SqlPool,
  make it optional 
* #24: do not use placement new/direct destructor calls: gcc5.2.1 bug? 
* Improve performance of operations with keys: optimized for int IDs
* micro_http: Support setting back log size on a listening socket
* Adjust logger format
* Simplify logic of SqlPool
* Logger: get/set/check the log level
* ElementTree: easy access attributes with @ prefix
* Update micro_http server and TcpSocket wrapper class
* important: start a transaction on first select if explicit transaction
  is required;
* pool: reopen a DB connection when got a DB error and no activity seen yet
  on the connection;
* micro_http: added HttpHeaders class implementation in Auth example;
* micro_http: analyze Content-Type more correctly;
* micro_http: allow to set response body with no additional headers.
* Fix XInclude processing for LibXML2
* fix broken object construction for explicit joins;
* rename class ObjectList -> DataObjectList
* added test for explicit joins
* do not thow from destructor even if a connection fails to rollback