deleted redundant Nest patch and incorporated merge patch into pipeline builder. not sure what i think about that.
code cleanup (try to use reviseHistory instead of manual machinery)
pretty printing for Selectors (in progress)
Merge branch 'master' of github.com:slamdata/slamengine
nicer errors for Pipeline phase
Remove JoinTraverse.

Build the direction map directly.
Merge branch 'master' of github.com:slamdata/slamengine into prettify
Merge pull request #73 from sellout/remove-JoinTraverse

Remove JoinTraverse.
Merge pull request #74 from sellout/minor-fixes

Minor fixes
don't use Any
let the caller worry about converting the annotations to strings
Merge pull request #72 from mossprescott/prettify

nicer errors for Pipeline phase
use String instead of Any
Show instance for Selector
Merge branch 'master' of github.com:slamdata/slamengine into prettify
Merge pull request #75 from mossprescott/prettify

More pretty-printing for debug
new approach to tree rendering
use NodeRenderer as a proper type class
NodeRenderer instances for Pipeline and its components
label Results in the output; show '...' only if there are actually more results that aren't shown