first stab at generic document

this will become the base for advanced parsing and modification of lilypond
source texts in the ly module.

Document will be inherited from later to support operations on QTextDocument
instances.

This is done so that all advanced manipulation can go to the ly module, and
can become available to commandline tools using the same module, without
that the ly module depends on Qt or Frescobaldi.
Merge branch 'master' of github.com:wbsoft/frescobaldi
wip
wip, basically working
Merge pull request #306 from PeterBjuhr/master

Typo fix
wip
lydocument provides the ly.document API for a Frescobaldi document (QTextDocument)
better
Merge branch 'master' of github.com:wbsoft/frescobaldi
Update prefs_lilypond.md: dragging include paths

closes #307
add Runner, improve doc
Merge pull request #308 from uliska/include-paths-help

Update prefs_lilypond.md: dragging include paths
add ly.document.TokenCursor and TokenIterator

they are like tokeniter.Runner and tokeniter.Source respectively.
Merge branch 'master' of github.com:wbsoft/frescobaldi
wip
wip, cursor updates position, doc love
add few Cursor methods
add DocumentBase.tokens_with_position
a wip stub for rewriting the rhythm stuff to use the new ly.document infratructure
make the token iterators capable of either using tokens() or tokens_with_position()