Merge pull request #5 from bgamari/master

Add matrix addition/subtraction and minor style cleanup
minor version bump
Added some verbage to liftU2
2x2 identity matrix.
Added the diag function to make diagonal matrices.
Renamed diag to kronecker.
Additive []. More aggressive inlining for Additive instances.
Additive ZipList
Switching to liftI2 to make the previous Additive [] instance valid.

* instance Additive ZipList
Merge branch 'master' of github.com:ekmett/linear
Merged my ZipList instance with John's
Additive Maybe
Improved Additive Maybe
Maybe CHANGELOG
Preliminary GAdditive for GHC.Generic Additives
GAdditive Par1
Switched to a Generic default for Additive to avoid 'false positives' where it used the wrong applicative.
instance Additive Vector
CHANGELOG for Vector
instance Metric Identity