Investigate Fixed Size Arrays

[JaredCrean2]

There has been some talk in the Julia issues about a fixed size (ie. compile time sized) array, which could potentially be much faster than regular arrays (whose sizes are not known until runtime) for small sizes. Flux jacobians come to mind as one place where this would be beneficial, although there may be others as well.

See discussion here: https://goo.gl/ERGCVZ
and here: https://goo.gl/YYlP1P

[JaredCrean2]

Currently, these arrays are heap allocated, which reduced their utility for these arrays. What we really need is a static array equivalent to the C code double arr[4], so this issue is a low priority until that gets figured out.

[JaredCrean2]

Looked into this, currently the length of the array cannot be a variable, which makes things difficult for functions that need to work in 2D and 3D.