functions to support parsing by a section by its children. Incomplete.
Merge branch 'master' into parse-section-children
parsing every children of section; system break support; basic infrastructure for system break support
render instructions (renderWith) for ecah staff
inserted lots of debug messages. To avoid them set log level to 4.
some comments regarding ties
Merge branch 'parse-section-children' into ties
Changed tie in the last measure embracing three notes. Added <tie> without endid in last measure
Implemented note dictionary (notes indexed by xml:id)
added EventReference and EventLink
global container for ties containing EventLink objects
support for @tie attribute [tests pass]
Merge branch 'ties'