Ergonomic language features and lib cleanup

+ let bindings
+ where bindings
+ do notation

I explored enough of the alternative language design space and decided
that we should commit fully to Lambda style. That means no more highly
tacit/concatenative point-free/partial programs as default. We'll keep
taking advantage of those capabilities when it makes sense, but the
library will continue to see massive overhauls.

tricu-apps/arboricxServer.tri

@@ -13,7 +13,7 @@
 -- Example usage:
 --   curl http://localhost:8080/
 --   curl http://localhost:8080/_arboricx/health
---   curl -X POST --data-binary @mybundle.arboricx http://localhost:8080/_arboricx/bundles
+--   curl -X POST --data-binary @mybundle.arboricx http://localhost:8080/_arboricx/bundle
 --   curl http://localhost:8080/_arboricx/bundle/hash/<hash>
 
 main = io (thenIO