gefs docs: could use explanation of what all the different gefs* functions do

[sckott]

@potterzot for the next milestone, no rush

e.g., gefs_times and gefs_ensembles were introduced in #328 , but it's not clear what they do , they are in gefs tests though, so thanks for that.

in addition, current parameters could use more explanation. for examle, for ..., you have

... additional parameters passed to the connection.

maybe you could say what kind of parameters users could pass in and how (i.e., in a named list? some other way?)

[sckott]

closing as gefs functions are now defunct