Missing `\` methods

Methods for `\` with non square matrix are missing:
```julia
using StaticArrays
A = @SArray randn(3,2)
v = @SArray randn(3,1)
Array(A) \ Array(v) # works
A \ v
```
```
DimensionMismatch("right hand side B needs first dimension of size 2, has size (3, 1)")
```