Compressed (gzip) files are not handled.

[skinkie]

The tool does not report, problems with processing compressed files

go run cmd/*.go validate -i /var/tmp/tec-netex.xml.gz

Decompressing manually does report output.

skinkie@thinkpad ~/Sources/DATA4PTTools $ go run cmd/*.go validate -i /tmp/test/tec-netex.xml 
┌ tec-nete ─╼
│ frame-defaults ...          ok
│ journey-pattern-timings ... failed with 2728 errors and 0 warnings
│ passing-times ...           ok
│ stop-point-names ...        ok
│ xsd ...                     failed with 1 errors and 0 warnings
└───╼

Expected: since libxml2 handles compression without an issue, this must work.

[lekotros]

This issue is fixed in #15