Memcached extension provided by CI env.
Adding build steps in CI depends.
Better progress indicator in CI depends.
Move PHP requirement in CI depends.
Use PHP_EXT in CI.
Refactoring CI depends to use method per extension.
Adding ability to install zendopcache in CI.
Add zendopcache to CI build matrix.
Adding default build to CI matrix.
Adding redis to CI matrix.
Exclude incompatible build xcache + PHP 5.5.
Addign apcu to CI build matrix.
Correct docblocks in CI depends.