linter first pass

[akhenakh]

First pass at Go linters, also see #5

tests are passing

[joshuaferrara]

See my comment in #5 , but the gist of some of these unused variables seems to be that they're actually meant to be outputs of the function. Rather than deleting these, we should return them and set values appropriately wherever these functions are called. It'd be best to look over the C++ source code (specifically sgp4unit.cpp) at https://www.celestrak.com/publications/AIAA/2006-6753/ and modify the call/returns of functions where necessary such that the output values are piped throughout the algorithm correctly. This was a total oversight on younger-me's part...ugh.