Additional methods regarding coordinate transformation.
- 
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.