Ability to disable key tracking

Fix #1550
Updated CHANGELOG
Fix fatal typo in phalcon_mvc_router_group_add_helper()
Fix #2071
Test case
Merge pull request #2075 from sjinks/memcached

Ability to disable key tracking for Memcache/Libmemcached backends
Merge pull request #2076 from sjinks/router_typo

Fix fatal typo in phalcon_mvc_router_group_add_helper()
Merge pull request #2077 from sjinks/issue-2071

Fix Array to string conversion in Phalcon\Http\Response::redirect()
Clean up #include
Replace placeholders even if the string is not in the language content

Fix #2044
Test case for #2044
Updated CHANGELOG
Bug fixes
Fix build generator
Regenerated build/
Bug fixes for clang
Regenerated build/
Cosmetic code fix
Merge pull request #2080 from sjinks/issue-2044

Replace placeholders even if the string is not in the language content
Fix #2081