Bump version number to 0.4.1
Fix Composer branch alias name

As per Composer documentation, branches are considered unstable. The
'3.3/master' branch was set as development branch in the composer.json
file, while it's actually stable branch.

Set '3.3/develop' instead of '3.3/master' branch as development branch.
Reword README contributing guideline
Add empty line at the EOF

As per coding standard.
Merge branch 'hotfix-3.3/master' into 3.3/master