underlined titles are now syntax highlighted in editor

[baudren]

Fix for #67. So far, only underlined titles are considered, and nothing is done for inline ones.

[landscape-bot]

Repository health increased by 0.13% when pulling dc22d72 on 67-SyntaxHighlighting into 99d8b2b on devel.

• No new problems were introduced.
• 1 problem was fixed (including 0 errors and 0 code smells).

[landscape-bot]

Repository health increased by 0.08% when pulling 5cd0762 on 67-SyntaxHighlighting into 99d8b2b on devel.

• 1 new problem was found (including 0 errors and 0 code smells).
• 1 problem was fixed (including 0 errors and 0 code smells).