Global refactoring

Signature of all constructors was unified
Method "load" now accepts arguments to generate data when cache expired
Entries now never expires instead when cache entry expired library returns expired data and attempts to generate new data
Temporarily removed PDO and MongoDB drivers
Autoloading was changed to PSR-4
Fix Travis-CI build errors
Fixed bug with MEMCACHE_COMPRESSED flag in last version of php-memcache
Refactoring and bugfixes

Added callback lock timeout
Fixed data generation when entry expired
Fixed redis drivers
New tests
Added CHANGELOG file
Added some docs
Added APC cache and now try to build library under HHVM
Changed HHVM to PHP 5.6 because Travis-CI fails while trying to install PHP extensions
apc.enable_cli in Travis CI
Method «load» was refactored. Bugfixes in XCache drivers
Bugfixes in Apc drivers
Improved performance of «doLoadMany» method in Redis driver
Trying to fix build errors
Fixed another one bug in Redis driver
Must select redis object instead iterating through connections
Improvements, fixes and tests

Method doLoadMany in Memcache, Memcached, Predis and Redis drivers was improved
New test was added to check the result of loadMany method when keys doesn't exists
Attempt to run XCache tests on Travis-CI
Fixes in APC and XCache drivers and Travis build script
Path to ini file for Travis CI
Travis CI again
Continue with Travis CI