Fix typos throughout the source code

[NeeEoo]

There were some inconsistencies with British and American english, but I'm not gonna fix that, since its technically correct, and I don't know what language the documentation is supposed to be.

[NeeEoo]

There were also some stuff I noticed, cpp spells it finalize and eval spells it finalise

[Simn]

Thanks! It's a bit scary how many typos there were...