Tidy up code / add comments for Eta
Tidy up Beta, add some comments
Rename eta subst lemmas and reintroduce eta_par_substitutive

Turns out it's needed after all!
Add a few auxillary lemmas about lam_k
Add proof of main lemma
Add to-be-proved lemmas on beta and beta_par
Add all necessary lemmas on the various beta closures

Work in progress, they should be moved to the Beta module
Move facts about beta to the Beta module
Merge pull request #18 from knuton/progress

Some progress, some beta stuff
Add one more lift_lift_rev lemma

Proof shamefully copy-pasted from dblib.
Add stubs for some more eta facts
Add proof of eta-postponement!
Add proofs about eta's
Add proof that eta_par is substitutive

Final `admit` (except for the lift / subst lemmas) eliminated!
Prove last admitted lemmas
Fix and prove lift_subst_semicom
Rename lift_subst_semicom into lift_distr_subst

Because that's what it is.
Merge pull request #19 from knuton/more_lift

Add one admitted lift_lift_rev lemma
Merge pull request #20 from knuton/final_touches

Proof of Postponement theorem and remove all admits
Merge branch 'master' into gh-pages