D.TwoD.Layout.CirclePacking: remove deprecated CircleFrac constructor
bump version to 0.7 and bump -core and -lib deps
Turtle.Tests: arguments to arcLength are now flipped
Turtle.Internal: bug fix: closeCurrent now produces only one new path

The problem was the call to 'setPenPos', which not only reset the pen
position but also created a new output path from the current path;
closeCurrent then proceeded to add a closed version of that path as
well. I.e. the problem is that 'setPenPos' is a 'smart' function made
for consumption by users of the API; all we want to do in closeCurrent
is *literally* set the pen position, and nothing else.  So, now that's
exactly what we do, which makes the code simpler anyway.

Fixes #13.
add CONTRIBUTORS file [ci skip]
CHANGES for 0.7 [ci skip]
Add initial version of Diagrams.Lens contrib module
Make type signatures simpler and more consistent
Alphabetize! (it was already close to alphabetic, might as well make it properly alphabetic)
update tested-with field: dropping support for 7.0 and 7.2 [ci skip]
add release date [ci skip]
check in some old tests [ci skip]
Make Diagrams.Lens build with ghc 7.6