hg: jdk9/sandbox: Update markdown to better match pandoc markdown.

[magnus.ihse.bursie at oracle.com]

Changeset: 893c9ab81b17
Author:    ihse
Date:      2017-03-08 00:14 +0100
URL:       http://hg.openjdk.java.net/jdk9/sandbox/rev/893c9ab81b17

Update markdown to better match pandoc markdown.

! common/doc/building.html
! common/doc/building.md
! make/UpdateBuildDocs.gmk