Feature/write geqdsk file

[mgyoo86]

Fixes the format for the header and numerical data:

• %-48s for description (including time at the last)
• %4d%4d%4d for idum, nw, nh
• %16.9E for numeric data without whitespaces

Since the writeg function takes the description as the keyword argument,
one can define and pass their own descriptions (except for the time) outside of the EFIT.jl.

[bclyons12]

Closing in favor of #19 since I can push to your fork