Various typo and grammar fixes in non-code files

[Ayesh]

• Replace Github with GitHub.
• Replace windows with Windows
• Replace advice with advise where a verb is used.
• A few fixes on removing repeated words.
• Replace a HTTP with an HTTP

[bagder]

github in lowercase should probably be removed from .github/scripts/spellcheck.words so that the CI jobs better can detect this mistake going forward.

The use of a HTTP... is used in numerous more places if you want to fix it even more. A fair share of them in source comments:

$ git grep -i ' a http' | wc -l
86

[Ayesh]

Awesome, I will get to it and push to the same PR. Thank you.

[Ayesh]

I force-pushed (diff)with the rest of the s/a http/an http/ patterns, and manually double checked every chunk. I also capitalized a couple http words in the comments to HTTP where appropriate.

This seems to be all of the typos with it, at least upto cd95ee9.

Apparently the spellchecker picks up on correct GitHub URLs as a typo; not sure what to do.

[bagder]

But it made two lines too long:

./url.c:1384:81: warning: Longer than 79 columns (LONGLINE)
         /* The requested connection does not use an HTTP proxy or it uses SSL or
./urldata.h:923:81: warning: Longer than 79 columns (LONGLINE)
      struct only because we can do just about any protocol through an HTTP proxy

[bagder]

Thanks!