enter() a buffer so display will refresh
Add CyclableOption class

This paves the way for context statuses, which can be cycled among 'include',
'exclude', and 'none'.
Commands & API functions to alter context settings
Grab libvtd which can do ContextList()
Display contexts (with highlighting and counts)
Map +/- to mark contexts as (in/ex)cluded
Map '/' to clear context from (in/ex)clude lists
Map '*' to toggle context (in/ex)cluded (+none)