and not as a string.
Changed name of the file TypedSymbol to types.
Fixed usage of dtype accordingly, however i might not have found every
usage of dtype.

- support for different #ghost layers at each coordinate limit

- LoopOverDomain changed to be able to loop over rectangular sub-region of field
- support for slicing with makeSlice

- added sphinx files for documentation generation
- collected kernel creation functions in new "cpu" and "cudagpu" modules