package: force sequential builds in Jenkins.

Follow-up to dd263c4ee1acf3767cdfcaeb4fc4454206f0f181, which didn't help
at all.
Utility: update Resource documentation.

We are asserting for not found resources now.
Utility: test filename consistency.
Utility: properly test Resource compilation with empty files.

Compilation of the generated file fails with "error: zero-size array
'resourceData'".
Utility: fix Resource compilation with empty data.