Sync with upstream @ fc3f811c

This PR was automatically generated to merge changes from en.javascript.info at fc3f811c

Conflicted files in this PR have labels ">>>..." with both sides of conflict. If you merge this PR, you'll need to examine the listed files and resolve conflicts.

Alternatively, you can close this PR and merge conflicting changes manually.

The following files have conflicts and may need updates of the translations:

[ ] README.md

To merge changes manually (instead of merging this PR):

Add remote upstream that links to the English version (only needs to be done once)
- git add remote upstream https://github.com/javascript-tutorial/en.javascript.info
Commit all current work locally and git checkout master
Pull the recent changes from the English version:
- git pull upstream master
Deal with the conflicts. If a conflict touches a few lines, then just fix it. Otherwise, following commands can help:
- Checkout your (translated) version of a file/folder at the given path (removes all upstream changes):
  - git checkout --ours <path>
- See the diff, what changed in the upstream file since branches diverged:
  - git diff --word-diff master...upstream/master <path> (please note: three dots in the command)
- Then you can examine the changes in upstream and add them manually
When conflicts resolved, commit them and git push origin master

Please ignore changes in README.md (git checkout --ours README.md && git commit -m ignore README.md).

This PR will be closed and replaced with a new one in a few days.

javascript-tutorial / ka.javascript.info

Sync with upstream @ fc3f811c #13