Musicxml

Release together with musicscore2

Bug fix: `XMLChildContainer.add_element()`: if container has a parent_element and container gets a duplicated parent,
duplicated parent
replaces parent_element's container if needed. (Necessary for `XMLEncoding`)

`README.md` is updated to include XMLElement dot operators as shorthand for getting or setting a child.

doc strings added to `XMLElement`

`XMLElement.get_class_name()`: removed. Use `XMLElement.__class__.__name__` instead

Bug fix: `XMLElement.get_parent()`: if XMLElement is a child returns now the parent XMLElement.
`Tree.up`: returns `Tree.get_parent()`
Bug fix: `XMLElement.remove(<child>)` removes duplications in `ChildContainerTree` if necessary. Bug
fix: `XMLElement.value` can be set to
None.
`Tree.get_leaves()`: added

Bug fix: `XMLElement.remove()`: remove_duplicate is now called after removing child. Indentation: changed from 4 spaced
to 2 spaces in order
to be consistent with finale's musicxml export.

Bug fix: `XMLChildContainer.add_element()`: if container has a parent_element and container gets a duplicated parent,
duplicated parent
replaces parent_element's container if needed. (Necessary for `XMLArticulations`)

`XMLElement.value` renamed to `XMLElement.value_`
`XMLElement.value_` will be checked immediately also for XSDComplexTypes

`XMLElement._check_value()` sets `self.TYPE.element` to self
`XSDComplexType` and `XSDSimpleType`: `element` attribute and `_get_error_class()` method added to be able to give a
better error message.
error messages improved.

`XMLElement` dot operator: shorthand to set and get a child `XMLElement.Type`: a class attribute to set ComplexType for
an `XMLElement`.

Bug fix: `XMLElement._SIMPLE_CONTENT`: is used to validate value. Using XSDSimpleTypes as parent was not the right way
to achieve this
validation

`XMLElement.<attribute> = None`: removes attribute if needed.

`XMLElement.remove(<child XMLElement>)`: removes child

`XMLElement XMLElement._unordered_children`: list to accelerate finding children if order of children is not important

`XMLElement.get_children(ordered=True)`: ordered False returns XMLElement._unordered_children

`XMLElement.find_child(ordered=False)` and `XMLElement.find_children(ordered=False)` added.

This version is the first uploaded version to PyPI