Moved vim mappings to repeat a visual selection into <leader> mappings

Mapping over the regular . operator had side-effects when trying to
repeat some things such as indentation.

Added a sister-mapping for repeating a macro over a visual selection.
Documented SplitItems Vim function; added user input

Also fleshed out a proof-of-concept function to join lines inside a text
object.
Replaced pubkey for burke