Generic names in C bindings

[skosukhin]

Currently, certain subroutines are exposed via C bindings under very generic names, e.g. interpolation. That might trigger a name collision in a user application.

A possible solution is to come up with some common prefix and use it for all public functions of the library, e.g. rrtm_interpolation.

[RobertPincus]

@skosukhin Thanks, this is a good idea. I'll try to implement in March some time.