Add YAML template expansion script and use it for .travis.yml.

[iphydf]

This change is 

[robinlinden]

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Reviewed 7 of 7 files at r1.
Review status: all files reviewed at latest revision, 1 unresolved discussion.

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tools/expand-yaml, line 121 at r1 (raw file):

                     if $v eq '???';
               }
               

Stray spaces.

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