Catch mp3 file of specified podcast through proxy
for usage, see the doc inside py file
''' Q: + how to receive multi-args after one opt?
+ TODO: update doc
+ how to inherient default arg?
+ request = urllib2.Request(url)
request.add_header("Range", "bytes=%d-%d"%(1024, 204) #指定下载文件的范围
opener = urllib2.build_opener()
data = opener.open(request).read()
+ http://stackoverflow.com/questions/22676/how-do-i-download-a-file-over-http-using-python
+ use `If-Modified-Since`
'''
