Skeleton XML building is very slow

See #186, release log:

• 3eb7cb6 by @yegor256: #186 null appender
• dcc8248 by @yegor256: #186 logs
• 534aea0 by @yegor256: #186 less logs
• f861826 by @yegor256: #186 org.jpeek.skeleton
• 35a32ca by @yegor256: #185 more logging
• 7a9b516 by @yegor256: #185 logging
• 0a93cbd by @yegor256: NaN in MMAC
• da76b15 by @yegor256: NaN
• 76481d4 by @yegor256: pgfplots
• d9bb20b by @yegor256: more scripts
• 501c18e by @yegor256: more scripts
• 58fe8e4 by @yegor256: step 5
• b57f576 by @yegor256: #162 deployment to web explain...
• 8288758 by @rultor: Merge branch '__rultor'
• 119e6ba by @rok-povsic: Removed not needed warning sup...
• e4b1399 by @rok-povsic: Clarified a puzzle. #114
• 6f7154b by @rok-povsic: Resolved conflict with master ...
• 868ad48 by @rok-povsic: Merge branch 'master' into mis...
• 02be3e4: Merge branch 'master' into iss...

Released by Rultor 1.67, see build log