pretty printing for Selectors (in progress)
Add more join compilation tests.
Fix reversed nested projections.
[minor] Reformatting.
[minor] Reformatting.
Merge pull request #71 from sellout/fix-nested-projection

Fix nested projection
nicer errors for Pipeline phase
Remove JoinTraverse.

Build the direction map directly.
Merge branch 'master' of github.com:slamdata/slamengine into minor-fixes
Merge branch 'master' of github.com:slamdata/slamengine into prettify
Use CompilerM instead of StateT more consistently.
[minor] Remove unused variables.
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