Sets up Gnus messaging service for Gmail and RSS.

Uses the `~/.authinfo' entry `email', which looks like this:

  machine email login grinn.amy@gmail.com password **** port imaps
  machine smtp.gmail.com login grinn.amy@gmail.com password **** port 587

The password is an App password generated here:

myaccount.google.com/apppasswords

Gnus enters `topic' mode which can be rearranged using commands
prefixed with `T'.  To get a list of these commands, type `T ?'.
To toggle `topic' mode, type `t'.

To send a new message, type `m'.  The Insidious Big Brother
Database (BBDB) will auto-fill the `To:' field when pressing
`M-TAB'.  To add a new entry in BBDB, use the command
`bbdb-create'.

Org mime can be used to send HTML email.  From within an Org buffer,
narrow to the subtree you'd like to export with `C-x n s' then call
Org mime with `C-c M-o'.  `C-c M-o' can also convert a message
buffer written in Org syntax into html.

For reading html mail, SHR colors are turned on by default but can
be toggled with the backtick key.

While in Gnus, org-capture-templates are overridden by
gnus-capture-templates, defined here.  The backslash key will move
a message into a new group and then capture it.  To capture a
message without moving it, use C-c c.