Sjkabc

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* format_abc() wraps header lines prefixing them with '+:'.

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* format_abc() will not include empty header lines.

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* Added support for continued info field lines (+:)
* Added factories for testing
* Unittest replaced with pytest
* Tune.format_abc() will no longer include empty info fields
* Add strip_slurs() which removes slurs (parentheses) from string. This function is called by expand_abc.

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* Fixed bug introduced by the Tune.abc and Tune.expanded_abc changes in last release
This bug broke Tune.format_abc()

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* Fixed bug which caused Tune.expanded_abc never to be set

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* Added support for P: (parts)
* Added tune method format_abc which returns a properly formatted tune
* Added support for F: (file)
* Added support :: shorthand syntax (which equals :||:)
* Added strip_decorations()
* Added strip_gracenotes()
* Removed support for A: as it's deprecated according to the ABC standard
* Fixed Travis-CI setup
* The strip_ornaments is now deprecated. It has been replaced by strip_decorations and strip_gracenotes and will be removed in future versions.