Fix various feature bugs

[drammock]

This PR does a few things:

• fix bug with special-cases feature table (lookups were happening, but not being properly handled) (2a4306c)
• when building feature vectors, clicks are now handled like modifiers (not like base glyphs), which makes it easier to get the correct features (previously they were incorrect) (a1007e7)
• special-cases a few clicks that are hard to get right automatically (aspirated ejective clicks) (fa0d362)
• stop ignoring the retraction diacritic on t and d (affricate features are unchanged, and now some australian languages have proper feature distinguishability) (8e7355a)
• generally improves the iterative feature-vector-building process, which results in a few other feature vectors changing (mostly pre-nasalized stops or affricates, they gain one or a few contour features). I consider this also a bugfix (it makes sense that, eg., nts would have a contour feature for [strident] or for [nasal]
• adds a .lintr file so my IDE isn't full of wiggly blue underlines while I code (if you don't want this I can add it to .gitignore and just keep it locally)

[drammock]

This is ready for review/merge @bambooforest. It doesn't fix everything but this PR is already starting to sprawl (was initially supposed to just fix click problems); will continue this work in a follow-up PR.