New stuff

Not ready to merge.

### New Measure changes

- `lineWidth` and `dashing` attributes are no longer tied to `V2` so they're moved to 'Diagrams.Attributes'
- `Text` is now wrapped in `ScaleInv` and gets scaled from `FontSize` by backends.

### Generalised SizeSpec

- Moved to `Diagrams.Size`
- `SizeSpec v n` is now a wrapper over `v n`
- extracting a `SizeSpec` returns `v (Maybe n)` with only strictly positive values
- `Diagrams.TwoD.Size` has some specialised functions.

### Intersections (unfinished)

- cubic - cubic using Bézier intersection, cubic - linear using Bernstein polynomials (adapted from @kuribas's `cubicbezier` package) and linear-linear using linear interpolation.
- would also like boolean path operations (kuribas mentioned it on [irc](http://ircbrowse.net/browse/diagrams?id=54191&timestamp=1409163819#t1409163819))

### Projections (unfinished)

- Only works on things like `Path` (projecting a `Diagram` would need special a backend)
- `LinearMap v u n` used for orthogonal projections
- `Deformable v u n` used for perspective projections