Backslash after alias causes 'Invalid path alias' exception in `\yii\BaseYii::getAlias`

Added support for arbitrary operators to Query::filterWhere, added support for arbitrary operators to Sphinx extension

- Removed `FileLoader` and used `\Twig_Loader_Filesystem` instead.
- Added support of Yii's aliases.
- Added `set()` that allows setting object properties.

Updated guide

fixes #4482

not sure about L421

INSERT queries didn't work with first letter capitalized in table name.

double word "from"

Fixes #4409: Upper case letters in subdirectory prefixes of controller IDs were not properly handled

fixed broken code block

- Upgrade the documentation to match filter code
- Fix bad default behavior with Access-Control-Allow-Credentials
- Fix missing "s" in header Access-Control-Request-Method / Access-Control-Allow-Methods