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It takes a list of assignments to staggered fields and otherwise behaves like create_kernel.
The old create_staggered_kernel was not removed because all the optimizations still need to be ported over.

When storing fluxes on a staggered grid, the usual sign convention is that
fluxes point outward from the cell. Previously, we did not respect that as
staggered_access("E") would return the same thing as staggered_access("W")
would when called from the eastern-next cell. Now, when a field is declared
as STAGGERED_FLUX, it returns an accessor with a prefactor of -1 in that
case. The previous behavior where sign is not reversed is still useful when
e.g. storing sums (e.g. mean values) instead of differenes (e.g. finite
difference fluxes) on the staggered grid.

NW (-1/2, 1/2) and the like were previously mapped to the wrong cell

According to the documentation, 0 is W and 1 is S

hash should not be used in hashable_contents because even if we will use
a deterministic hash function we will end up non-deterministic since
hash is initialized with a random seed.

__repr__ of Field should look like

```
y: uint16_t[246,704,558]
x(3): float[20,40]
```

to match representation when using `pystencils.fields`

TextureCachedField was using `hash(...)` to disambiguate its instances.
However, `hash` is randomized and will hinder reproducible code
generation

- bugfix: loop counter of vectorized loop now correctly stored as SIMD vector with entries i, i+1, i+2, ...
- basis for in-kernel boundary handling

For sympy, oo s a number. So pystencils prints a type infinity a double
INFINITY as INFINITY.0