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add MultiParamTypeClasses pragmas for correctness

GHC is apparently OK with referring to MPTCs without enabling the
extension, but technically I think this is not correct, and
haskell-src-exts does not like it. See http://hpaste.org/83072 .
add more MPTC pragmas, and clean up pragmas & imports
remove technically illegal parens around constraint

GHC accepts this but it makes haskell-src-exts unhappy (and
haskell-src-exts is technically correct here, according to the
Report).
bump version to 0.6.1
clean up whitespace and imports
add Eq, Ord, Show instances for SizeSpec2D
pragma/import cleanup
depend on NumInstances 1.2 and import only Data.NumInstances.Tuple

Fixes #48.  Now we only export the Num (and Eq and Show) instances for
tuples.  Anyone wishing to use Diagrams.CubicSpline with a vector
space built over functions can import Data.NumInstances.Function themselves.
ignore .diagrams-cache
change Data.NumInstances import in Diagrams.TwoD.Types (see #48)
use dual-tree and monoid-extras from Hackage for Travis tests
Travis: cabal update before starting build
use onBasis in renderTransf, rather than duplicating code
add function onBasis specialized to R2

onBasis helps backends construct a matrix representation
of a Transformation
Add haddock doc for onBasis
Merge pull request #78 from bergey/matrix-basis-rep

Matrix basis rep
Merge branch 'master' into generalize-R2