Fix trailing newline in default instance print method

The previous fix was lost with the merge from #6 at
c590b343abab930d63f29bfcdd2b2d0f84a84f01.
Merge pull request #11 from gaborcsardi/fix/trailingnewline2

Fix trailing newline in default instance print method
Add test for super inheritance structure
Rename test file
Partial fix
Separate fields from methods on class creation
Partial fix for inheritance
Fix printing of generators
Better line breaks
Slowly approaching inheritance fix
Correct inheritance for non-portable. Fixes #10
Correct inheritance for portable. Fixes #10
Consolidate create_super_env functions for portable and non-portable
Merge branch 'super-fix'. Fixes #10
Add Portable vignette
Update README
Add assignment example to Portable vignette
print should return object invisibly

According to the print manual page. Also added this to
the print method in the Intro.
Fix vignette typo
Merge pull request #14 from gaborcsardi/fix/printreturn

print should return object invisibly