* Get rid of open_darwin
	It just lead to code duplication for a simple one string change.
	Instead we query it during initialization
* Accept user provided arguments
	"open" on MacOS accepts things like -A to use a specific application
	Pass trough arguments the user provided in order to facilitate this
* Refactor the function to a struct
	This makes it more convenient for the caller and avoids signatures like
	lib.OpenFile(nil, u.String(), nil) which are fairly unreadable

The `pin-tab` and `unpin-tab` global commands were added in 3156d48
but were not previously documented.  This documents them in aerc.1.
I added them with the other tab commands, which appeared to be grouped
as a logical unit.

Allow styles to be layered over a base style. The list of styles to
apply is layered over the base style in order, such that if the layer
does not differ from the base it is not used. The order that these
styles are applied in is, from first to last:

msglist_default
msglist_unread
msglist_read    (exclusive with unread, so technically the same level)
msglist_flagged
msglist_deleted
msglist_marked

So, msglist_marked style dominates.

This fixes an issue where the msglist_deleted style was not being applied.