Centralized (compiler) warnings

[charlesgregory]

From #55, moved here for separate discussion.

I would also like to see compiler warnings when using direct integer coordinates within the library to indicate a developer may encounter off-by-one errors.

Not sure yet how I feel about this. Could be good, could be super annoying

Could potentially add a dhtslib.warnings. This would contain variables to be set at compile time and also report pragma messages. Then we could report only one (pragma) message? This would prevent excessive messages at compile-time. I would have to look into the whether this could even be done the way I envision it. These warnings could be used to warn if you are using dhtslib in performance mode (if we ever make one).