Remove/update mentions of gh-pages branch

[bbatsov]

@dsyme That's basically follow-up of the rename of the gh-pages branch you already did.

[dsyme]

Resolve conflicts?

[bbatsov]

@dsyme Done!

Btw, looking at your changes, do I get it right the F# Foundation is dead and we need to cleanup mentions of it?

[dsyme]

@bbatsov Not quite - it's more that the foundation is now more of a background legal entity - it exists but is not something for active participation or branding. Other community efforts are doing a better job on that.

[psfinaki]

@bbatsov you're doing an amazing job - thanks for giving fsharp.org an update. With time, we get tunnel visioned by how things are and your fresh look is very helpful here!

[bbatsov]

@psfinaki Thanks for the kind words! It's always nice to contribute what I can to languages that I enjoy, and their respective communities. And it's great to see that here everyone's so open to various small improvements!