Merge pull request #664 from isivigno/DSLsubsegmentRelease

DSLSsubsegment release
wip
Fixing doc and perf issues in DSLSubSegment
Doc + changelog
Merge branch 'docMinor' of https://github.com/dcoeurjo/DGtal into DSLsubsegmentRelease

Conflicts:
	ChangeLog
merge
add simple test file