Hypnotoad: Added read_idam routine

Reads a magnetic equilibrium directly through IDAM, making analysis of MAST
shots quicker (no need for a & g files). Because IDAM can be quite fiddly
(firewalls and so on), usage is in two steps:

1. Use read_idam to get the data. Save as a variable 'rz_grid' in an IDL file

2. In Hypnotoad, restore this file ("restore R-Z"),