Dev code cleanup

[Merg1255]

@kapadia As mentioned in the README, the code file should be free from repeated code that spawns web workers.

[kapadia]

We have some repeated code when reading compressed images, which is why I haven't enabled reading them asynchronously. There is also some repeated code when swapping endian, but it's minimal. Have I missed something?

Avoiding this redundancy would mean another rewrite. Do you have any suggestions?

[Merg1255]

@kapadia I started this topic just to have in a plan for a rewrite. Since I'm using the JS version, the rewrite should be based completely on your preferences.