Use |deep_copy| in ternary operators when needed

Deep copying wasn't performed in assignments where the RHS was a ternary
operator, even when some of its branches would normally be deeply copied
if they stood alone. Similarly with |return| statements. This commit
fixes the problem.

Fixes #47.
README.md: Small updates

  * YaST *was* already converted to Ruby
  * yast2-core should be installed from YaST:Head, not YaST:Head:ruby
    (which no longer exists)
Add CHANGELOG
Update version to 1.0.1