change TimestepForcingJSON's modeled_timestep to be interval

[ghost]

fixes #117

[saeed-moghimi-noaa]

@zacharyburnettNOAA

I suggest to use a more descriptive variable name like:

ForcingTimeStep or ForcingInterval

[ghost]

@zacharyburnettNOAA

I suggest to use a more descriptive variable name like:

ForcingTimeStep or ForcingInterval

I thought about that, but it is already in a ForcingJSON object, or in a configure_atmesh.json or configure_ww3data.json file, so I figure it would be redundant as you know which file you are looking in. The full name in code is ForcingJSON['interval']

I was thinking of making it read_interval because that is the interval at which it is read by the model, in modeled time