Move yardoc configuration to .yardopts

Using `.yardopts` allows also external services such as Rubydoc.info
to pick up the correct Yard options.
The NEWS file is not available
Add yard-tomdoc to gemspec dependency
Merge branch 'yardoc' of github.com:gioele/coco into gioele-yardoc

Conflicts:
	Rakefile
Merge branch 'gioele-yardoc' into development
Add tomdoc plugin in .yardopts
Add Changelog file in documentation
Fix some typos in Changelog