[youtube] "youtube.com/name" can be a user or a channel

[pukkandan]

Please follow the guide below

• You will be asked some questions, please read them carefully and answer honestly
• Put an x into all the boxes [ ] relevant to your pull request (like that [x])
• Use Preview tab to see how your pull request will actually look like

---

Before submitting a pull request make sure you have:

• At least skimmed through adding new extractor tutorial and youtube-dl coding conventions sections
• Searched the bugtracker for similar pull requests
• Checked the code with flake8

In order to be accepted and merged into youtube-dl each piece of code must be in public domain or released under Unlicense. Check one of the following options:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

---

Description of your pull request and other information

Direct youtube URLs (youtube.com/name) now doesn't have to be a username but can be channel name. Closes #186

[someziggyman]

have no time to review it. maybe monday. maybe someone else can.

Seems to be a legit fix and works fine for the cases described. Links like this: https://www.youtube.com/zsecurity are going to work fine with this improvement. However, I'm not sure how it was generated. Clicking on various YouTube channels within YouTube all came up why a /c/someChannelName or /channel/somechannelid - https://www.youtube.com/c/PeterSantenello or https://www.youtube.com/channel/UCVPjtOVcnKaSRI8IO3KSetA

Doubt there's any risk approving and adding it to the next release. It works with all link formats, so it's definitely a good thing. Maybe, someone else can take a look and confirm with more expertise.
@pukkandan has done a great job

[pukkandan]

However, I'm not sure how it was generated. Clicking on various YouTube channels within YouTube all came up why a /c/someChannelName or /channel/somechannelid

@someziggyman Youtube allows to shorten /c/channelName to just /channelName. But they also allow /u/userName to /userName. So given a url such as /name, it not possible to tell whether it is a usename or a channel name. However, since all the code for downloading user and channel is the same, I just made it use the shortened URL itself for extraction. That way there is no need to know if it is a user page or channel page.

[pukkandan]

Made obsolete by #245