corrected app dir example and removed license code from example.

[Guide] Fix link

fix typo in the word Semantic

Improved the advanced app template documentation.

Fixes #3268: Fixed the bug that the schema name in a table name was not respected by `yii\db\mysql\Schema`

Not sure about the “for example…” paragraph under “usage”. Doesn’t read
well currently.

Fixes #2906: Added support for using conditional comments for js and css files registered through asset bundles and Html helper

[ci skip]

fixes #3255

Q: When attaching event handlers in the config, does it have to be an
anonymous function?

Moved “triggering” after “attaching”.

Cut a sentence that seemed both redundant and vague. Could just be me.

Fixes #3230: Added `yii\filters\AccessControl::user` to support access control with different actors

Update active-record.md

typo

typo in comments

property can be set via [[setComponents()]]

Added alternative way of setting up dev environment.

implementation checks for instanceof for additional swiftmailer
capabilities.

issue #2870

controller links application vendor to yiidev repo

Didn’t make any sense, particularly after the browser stuff. If kept,
I’d move it behind the other command-line reference.