The tags are stored in a dict now, which does not
have .append().

Implement a safe delete that works even if a given
tag is not present.

Useful to find nodes based on arbitrary constraints.

This can be used together with select:

for node in todos['done']:
	node.delete()

Improvements:
- shorter; less code duplication
- unicode clean
- simpler interface
- flexible iteration interface
- less chance to create an inconsistent data structure
  (e.g., have a note that ends with a ':')

Combine a select query with rendering the TaskPaper object to a string.

For example, consider the following example:

    td = TaskPaper.parse(open('/path/to/my/todo-list')
    print td.format(lambda nd: 'today' in nd.tags)

This will show all items tagged with @today _and their parents_,
just like the TaskPaper GUI will do when filtering by a tag.

The '@' sign was missing if a tag had a parameter.

Allows a node to be transferred between documents such that
all parents are transferred as well unless already present.

Much simpler and cleaner.

Fixes hwine/python-taskpaper/#1 on github
The TaskPaper app considers projects to be any line which:
 - does not start with '-', and
 - has a last non-tag character of ':'
when leading white space is considered part of the tag

These tests trigger the github issue hwine/python-taskpaper/#1

(Tests added after fix, so future bisecting always works.)

Taken from master branch from https://github.com/hwine/python-taskpaper.git

Needed to handle TaskPaper 3 saved searches...