prevent memory leak from RepoTreeModel
add initial support fot doxygen-generating

how to use it
1. cmake .
2. make doxygen
3. open docs/index.html
Merge pull request #329 from haiwen/doxygen

add initial support fot doxygen-generating
Merge pull request #221 from Chilledheart/patch-1

prevent memory leak from RepoTreeModel
use transfer mgr to manage upload/download tasks
display download progress in file table