docs, tests and bug fix for pull 122
minor #113 docs, tests and bug fix for pull 122 (joserobleda)

This PR was squashed before being merged into the 1.1.x-dev branch (closes #113).

Discussion
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docs, tests and bug fix for pull 122

This is a continuation of the pull https://github.com/fabpot/Twig-extensions/pull/112

- [ ] `doc/i18n.rst` now includes the `notes` usage and example
- [ ] Added 3 test cases for different `notes` combinations
- [ ] As `notes` adds an inline php comment to the compiled template line breaks should be removed

Commits
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5965f45 docs, tests and bug fix for pull 122