Remove top level directories from the paths in Doxygen log

Removing "docs/doxygen" and "interface" was both ambiguous (because it
wasn't immediately clear which file the message was referring to) and
insufficient because there are now Markdown files in the other other
directories used as Doxygen input too, and they still appeared with the
full paths.

Fix both problems by removing just the top level directory from all
paths and keeping all the rest.

docs/doxygen/regen.sh

@@ -222,7 +222,5 @@ fi
 # Doxygen has the annoying habit to put the full path of the
 # affected files in the log file; remove it to make the log
 # more readable
-currpath=`pwd`/
-interfacepath=`cd ../../interface && pwd`/
-cat doxygen.log | sed -e "s|$currpath||g" -e "s|$interfacepath||g" > temp
-mv temp doxygen.log
+topsrcdir=`cd ../.. && pwd`
+sed -i'' -e "s|$topsrcdir/||g" doxygen.log