Additional methods regarding coordinate transformation.

`coordtransform(`

`coordmapping`,`axes_to`, *`dims`)-
Coordinate transformation with

`coordmapping`into`axes_to`.ARGUMENTS

`coordmapping`(CoordMapping) : relation between the new and original coordinate systems. Mapping is defined from the new one to the orinal one. If the rank of the mapping is smaller than the rank of self,`dims`must be used to specify the correspondence. e.g., if the rank of the mapping is 2 and that of self is 3 and the mapping is regarding the first 2 dimensions of the three,`dims`must be [0,1].`axes_to`(Array of Axis) : grid in the new coordinate system. Its length must be the same as the rank of`coordmapping``dims`(integers) : Specifies the dimensions to which`coordmapping`is applied. Needed if`self.rank!=coordmapping.rank`

(neglected otherwise). The number of integers must agree with the rank of the mapping.