Config

[R5dan]

Supersedes #2209 with better implementation.

Changes:

• Deprecates all proxy, session and timeout in functions
• Adds yf.set_config
• Allows setting:
  • proxy
  • session
  • timout
  • url
  • language
  • region
• Adds deprecator for future use
• Adds docs for use of yf.set_config

[R5dan]

@ValueRaider what do you think? Happy to move yf.set_config if you can think of somewhere. I have deprecated all of the session, proxy and timeout (thats why its adding code not removing it but that can all go away in a few versions time)