Error when using `import`.

[Liam McGillivray]

I now have the Raylib functions working by using `toStrinz`.

I pushed some updates to the repository. I made the main project 
a source library so that I can experiment with different graphics 
library front-ends. I put have the front-end using Raylib in the 
`raylib_frontend` directory. It doesn't yet have any 
interactivity, but it should build and run successfully IIRC.

I don't know how best to organize the code. So far I have been 
putting the loop that runs during gameplay in the `Mission` 
function in `mission.d`. This function contains the arrays where 
sprites are stored. The code for unloading data from files is 
split between this function and `maps.d`. I was going to have a 
file in the main `source/` (not `raylib_frontend/source`) called 
`loadData.d` which would handle unloading from files, but then I 
realized that those functions would need write access to multiple 
variables, making it a not very tidy approach.

One possibility is to turn `Mission` into a class. The Mission 
object would control the Map object and other things during 
gameplay. The other possibility is to make a derived class of Map 
with more graphics-related functionality and more.