The go compiler can't help much with untyped int constants.
Even though the only valid constants are 0-3 it will happily accept 4 as input.

Let's let the go compiler worry about correctness here. This also allows people
not very familiar with the code to use it properly via auto completion.

+ Adds parsing of contextual ui sections to aerc config.
+ Add GetUiConfig method for AercConfig that is used to get the
  specialized UI config.
+ Add UiConfig method to AccountView to get specialized UI Config.
+ Modifies Aerc codebase to use specialized UIConfig instead.
+ Adds documentation for Contextual UI Configuration

Before, while the docs stated that template-dirs was a colon-separated
list, a delimiter was not specified in the struct tag, so it was falling
back to the default for the ini library (a comma). Also added a note to
the docs to clarify that templates are configured in the [templates]
section.

Note that, until we get color configuration, this means that the user *must*
have the %Z verb in the index format else it'll be horribly confusing
as no visual indication is provided

Complete email address fields in the message composer with an external
address book command, compatible with mutt's query_cmd.

Rather than showing completions inline in the text input, show them in a
popover which can be scrolled by repeatedly pressing the tab key. The
selected completion can be executed by pressing enter.

A new config options for accounts.conf (folders-sort) was added to
allow a user to choose which folders should be shown on top.
My use case was to avoid stepping into heavy, but rarely viewed folders
when cycling through other often accessed ones.

To test add this to your account.conf:

folders-sort  = INBOX,Sent,Archive

INBOX, Sent and Archive should then show at the top of your dirlist,
and all other folders should come next in alphabetical order.

%F now shows the auth name or recepient name/address if the
message is from you.