I/O Runtime Wishlist

[AaronDonahue]

There have been a number of feature requests regarding runtime I/O. This issue is meant to collect them all into one place so we can manage them.

• [ ] Check if list of output variables is valid - see #2246
• [ ] Compare ATM dt with the frequency of output. This is an issue when the output frequency may be smaller than dt.
• [ ] Make sure no two output streams will share a name (i.e. overwriting each other). This is a pretty edge case, so not high priority.
• [ ] Make sure all required keys are present. i.e. filename_prefix, grid, fields, frequency, etc.