add vimrc provided by Debian 7.4
add changes to vimrc
add vim plugins

* DoxygenToolkit 0.2.13: http://www.vim.org/scripts/download_script.php?src_id=14064
* fugitive 1.2: http://www.vim.org/scripts/download_script.php?src_id=15542
* gcov 1.0: http://www.vim.org/scripts/download_script.php?src_id=8141
* cscope_maps: http://cscope.sourceforge.net/cscope_maps.vim
* cscope_git: http://github.com/eherde/dotfiles