Re: modifying default behaviour of tremolo slashes (issue4636081)

[lemniskata . bernoullego]

Finally - new patch set uploaded.
Now it's possible to easily switch between different tremolo behaviours.
'Style' property is no longer used to choose between rectangular and
beam-like slashes - this is now done using 'shape' property.
'Style' property now influences both 'shape' and 'slope' of the slashes:
- style=constant produces beam-like slashes with slope .4 in case of
downstem flagged notes and slope .25 in all other cases,
- style=varying is equal to current default behaviour.

It's possible to choose a combination of those by setting both 'style'
and 'shape' properties.

Pdf demonstrating new behaviour:
http://lilypond.googlecode.com/issues/attachment?aid=17350003001&name=tremolo+new.pdf&token=4f500aee754e0419a28c61dc1a2abf6d

Please review. Suggestions on value names are most welcome!

http://codereview.appspot.com/4636081/