`xu` undoes the character delete`xu` undoes the character delete
Revert "`xu` undoes the character delete`xu` undoes the character delete"

This reverts commit fdbd28bfce426418331ac551f9e74e77e25d25da.
Revert "No longer maintain buffer-level :lines"

This reverts commit c9a3996ebb71a815df3f77273e19ece34bab6751.
Revert "`avi.normal-mode` doesn't access :lines"

This reverts commit af16e7d6ec3f629dd8fe89643b76fe532b5cd186.
Revert "More accesses to :lines through :changes"

This reverts commit ad2d4ae11df339a9e84994c7d49dcd20ea8d0594.
Revert "More line-wise access via :changes"

This reverts commit 4027370991b393d27eb6caa16ada9bc837f61a4a.
Revert "Get line count from :changes"

This reverts commit 1eb48a28d55ce0b5bf67c721ffc10d274c8b00ad.
Revert "Get a particular line from :changes"

This reverts commit 53d68d433c41d2876f5bb6d205f317c2cb922d02.
Revert "Use changes when writing buffer"

This reverts commit 22997515afd3b2133bb01d83d1ba183f02a8cf44.
Revert "Update buffer contents in both places"

This reverts commit 9d3ec03a4d2dceaa16e5128225c9cac32d35660f.
Rename `:changes` `:undo-log`, make start empty
Introduce `change` for making edits to lines
`xu` leaves the file the way it came`xu` leaves the file the way it came
Simplify and group change/undo
Use packthread 0.1.2
`u` tells us it's already at the oldest change`u` tells us it's already at the oldest change
`xxxuu` leaves first delete`xxxuu` leaves only first delete
`xu` leaves the cursor at 0,0`xu` leaves the cursor at 0,0
`ddju` leaves cursor at 0,0Undo places cursor at last edit
`ddGu` adjusts viewport to cursor`ddGu` adjusts viewport to cursor