one can now convert to branch traits

This is a downgrade of static safety, but is certainly an upgrade
in convenience. Now we don't have to spell out emulations for union types,
which are just mildly annoying in case of names, but close to impractical
in case of e.g. terms.
ensugars term placeholders
ensugars assignments via setters and updates
updates to a new build of scala.meta that fixes compound type prettyprinting
ensugars catch exprs
Merge pull request #13 from xeno-by/master

another test is converted and prettyprinted correctly