stop exporting Coordinates from Diagrams.Prelude

This is for compatibility with lens, as (&) is a rather important lens
operator and clashes with Coordinates.  Users who want the Coordinates
stuff can import Diagrams.Coordinates explicitly.  Still need to
update documentation to note this, and fix user manual examples,
gallery, etc.
note in documentation that Diagrams.Coordinates must be explicitly imported
Merge pull request #82 from diagrams/coordinates-noexp

Stop exporting Diagrams.Coordinates from Diagrams.Prelude
Big refactoring of segments and trails.

  * Segments can now be "closed" or "open"
  * Trails are "lines" or "loops", represented more correctly and tracked at the type level
  * Add a new 'Located' wrapper for adding locations to translation-invariant things
  * Change 'PathLike' to 'TrailLike', which now takes a Located Trail
Merge pull request #87 from diagrams/bee-coh-squashed

Big refactoring of segments and trails.
export convenience functions strokeLine and strokeLoop
cubicSpline does not actually need a Monoid constraint
D.Trail: export isLineEmpty and isTrailEmpty
Merge branch 'master' into parametric.

In particular, some non-trivial merging had to be done to incorporate
the major Trail refactoring (@705a9b28).

Conflicts:
	src/Diagrams/Path.hs
	src/Diagrams/Segment.hs
	src/Diagrams/TwoD/Path.hs
	src/Diagrams/TwoD/Segment.hs