add settings & download_mode define

Signed-off-by: Jack <jack.wgm@gmail.com>
add struct handle_reader

Signed-off-by: Jack <jack.wgm@gmail.com>
...

Signed-off-by: Jack <jack.wgm@gmail.com>
fixed compile for mingw

Signed-off-by: Jack <jack.wgm@gmail.com>
fixed compile error! remove handler reference.

Signed-off-by: Jack <jack.wgm@gmail.com>
Merge branch 'master' of codedoom.net:/git/avhttp

Conflicts:
	include/avhttp/multi_download.hpp