InputContainer: Fall cleanup ;).

Get rid of the doc & seqtext fields, as they are not actually used (nor
are they particularly useful, the event handler's name should be pretty
self-explanatory).

Also, tweak the key_events documentation to highlight the quirks of the
API, especially as far as array nesting is involved...

Random drive-by cleanup of the declarations of key_events & ges_events
to re-use the existing instance object (now that we know they're sane
;p) for tables with a single member (less GC pressure).

frontend/ui/widget/button.lua

@@ -190,14 +190,12 @@ function Button:init()
                 ges = "tap",
                 range = self.dimen,
             },
-            doc = "Tap Button",
         },
         HoldSelectButton = {
             GestureRange:new{
                 ges = "hold",
                 range = self.dimen,
             },
-            doc = "Hold Button",
         },
         -- Safe-guard for when used inside a MovableContainer
         HoldReleaseSelectButton = {