Checking function for inputs

[RyanDavies19]

In some cases, invalid values in the input files cause MoorDyn to crash with a segmentation fault. It would be good to implement a function that checks values to ensure they are valid and report an error if not. I believe this mainly applies to invalid output flags and invalid object numbers. There may be more that cause this.

[RyanDavies19]

If a user gives an output channel that has an incorrect object number, MD will seg fault. Example: requesting FairTen4 from a system with 3 lines.

Corresponds with:

MoorDyn/source/MoorDyn2.cpp

Line 1260 in 0a9a8aa

// TODO: add checks of first char of num1,2, let1,2,3 not