Consider switching to curl / wget for http(s) ftp #72

Why:

• multipart support
• auth/proxy support
• inferring filenames ( what Add providing location for fetch #56)

Issues:
@pombredanne mentioned it might be too heavy tool for the task
@JonoYang mentioned overhead of doing it via subprocess

Great page comparing wget vs curl
https://daniel.haxx.se/docs/curl-vs-wget.html

@pombredanne mentioned https://aria2.github.io/ as potential alternative which might be better than both curl wget