Merge pull request #1965 from mruz/2.0.0

Several fixes in 2.0.0
Merge pull request #1979 from mruz/2.0.0

Image fixes
Using latest zephir
Adding missing initializations
Merge pull request #1985 from mruz/2.0.0

Assets manager fix [ci skip]
Using latest zephir
Avoiding use  zephir_fetch_nproperty_this when is not safe
Avoiding use read-only zephir_array_isset_fetch when is not safe
Session start fix [ci skip]