feat: make HTMLtoPDF service open source

[hxtree]

Release HTMLtoPDF as open source software.

Notes: It's stable, works like a charm. Hopefully it will help out someone else. Seriously.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
-0.06%	∅

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (18b6847)	3579	1830	51.13%
Head commit (e530714)	3579 (+0)	1828 (-2)	51.08% (-0.06%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#449)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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