- add validation with yaml schemas and not juse json schemas.
	allow to have 'schema_file_json' and 'schema_file_yaml'
	in metadata and work according to that.
	modify the data files accordingly.
- add loading of url.
- removed now unneeded file support (left onyl url support)
- add installer for npm which works like this:
	$ npm install --quiet --silent htmlhint > /dev/null
	and works from a package.json and package-lock.json
	have a look at riddle-book project for example
- my cache is bad if the filename has a space in it.
- add a "make" builder for pydmt which depends on the Makefile
	and produces an "out/make.stamp" file and run it at the
	end of pydmt build under the venv ofcourse.
- disabled feature was removed.
- added ability to control log level from the command line.
- removed the various different imports from config/python.py and settled for just one import.
- add installer for gems which works like this:
	$ bundle install --local
	and works from a Gemfile and Gemfile.lock
	look at site-personal-jekyll.
- added option to remove packages in the apt builder.
- made sure pydmt will work in an empty folder.
