Marker file for catkin_make (#304)

First commit only writes a marker file. Possibly that is all you want to merge.

The third commit also makes use of the marker file, in case no explicit target path argument was passed to catkin_make.

I was not sure for which part you wanted a PR, so you can cherry-pick what you want. I am dispassionate about the filename, and about file vs. folder, so you can change to your liking.

I recommend using yaml or a folder because a likely future extention is to store metadata such as preferences or build configurations, and it would be bloat to have to store them in separate files next to the marker file.