show memory usage in percentages

See #110, release log:

• ccb602e by @yegor256: #110 text
• b1d69c8 by @yegor256: #110 done
• a793cf1 by @alex-semenyuk: #108 Fixed url
• 7edc75d by @yegor256: #105 link fixed

Released by Rultor 1.68.1, see build log