Merge branch 'master' into marshall

* master: (96 commits)
  compiler.cfg.dataflow-analysis: iterative dataflow analysis framework
  functors: add MIXIN:, SINGLETON:
  Add assoc-refine, which takes the intersection of a sequence of assocs
  compiler.cfg: Fix unit tests
  compiler.cfg.registers: minor optimization
  compiler.cfg.ssa: Cytron's SSA construction algorithm
  compiler.cfg.dominance: fix idom computation, compute dominator tree, compute dominance frontiers, add some tests
  Move conjoin-at from compiler.cfg.liveness to sets
  sequences.abbrev: add docs - not much, but a start
  sequences.abbrev: keep insertion order
  sequences.abbrev: more small refactoring
  sequences.abbrev: small refactoring
  sequences.abbrev: Initial commit
  opengl is for chumps
  alien.inline.compiler: help-lint fix
  parser: remove outdated unit tests that were superseded by tests in vocabs.parser
  vocabs.parser: add tests to assert that the correct errors get thrown
  ui.tools.listener: selecting a word from a completion popup now behaves like a USE: followed by a FROM:
  FROM: and RENAME: give a more meaningful error if the vocabulary does not exist
  compiler.cfg.stack-analysis: fix outdated tests
  ...