Improve Guide section on other editors

Mention racket-mode and replace the `raco planet` mention with
`raco pkg` instead.
pull in Gumby
initial commit
rename
try
more
First attempt at a "learning" section
Add Redex book too for better balance
Forgot Redex cover
Typo fix
improve navbar, text, add people & racketcon
todo list
minor learning section changes
add news, not happy yet
edit the top text a bit
a new news attempt
add a larger example
Fix learning section issue on mobile size
Remove todo item

(note: the book images should still be all sized to
 the same size, but this can be done later)
Start on RacketCon page example