* Renamed `draw_line_body` => `draw_line_main`
* Renamed `draw_gutter_text` => `draw_line_gutter`
* Added `draw_line_text` for *just* the line text

Solves #24

Fixes #14

Fixes #16

Fixed root:switch-to-* command

Before the fix navigation between nodes in the root
view was broken: the scale factor wasn't taken into
account. Switching in the right and down directions
was impossible for scale factors greater than one.

This prevents AltGr from being treated as the `alt` modkey. Previously
its default behaviour would have been overridden if the keymap had an
`alt+...` stroke bound