find: modul for search algorithms
find.py: set start level correctly
section.py: find methods for sections
file.py: find method for sections
block.py, source.py: find mehtod for sources
find: some small bugs fixed
find.py: simplify and remove unnecessary code
find: unit tests for find methods
Merge pull request #37 from stoewer/find-sources

Find functions and methods for sources and sections