Changelog and API docs corrected.

Merge branch 'master' into major

Merge branch 't/10644'

Updated translations, added Sinhala language.

Added information about Macedonian and Uighur translations.

Extra allowed content rules for xhtml-like output sample.

4.0.3 changelog corrected.

Changelog proof-read and corrected.

Changelog proof-read and corrected.

Updated CKEditor samples.