This commit changes the default keybindings for Home and End. It
also changes the InsertEnter action to InsertNewline (a better name)
although InsertEnter is still valid for backwards compatibility.
Closes#206
Tab is now bound to both IndentSelection and InsertTab.
There is currently no binding for OutdentSelection (the user can
bind that to their liking). Hopefully in the future it can be bound
to shift-tab but tcell does currently support that.
Closes#203