Zmid, Rcenter are not defined correctly in geqdsk2imas

[jmcclena]

geqdsk2imas assumes that Zmid and Rcentr are the geometric quantities of the boundary. However, in a geqdsk, ZMID is the center point for the EFIT grid, and RCENTR is the radial location where BCENTR is defined. I will work on a pull request to fix this.

[jmcclena]

Fixed with 294da61