Fix some potential errors and clean up the codebase a bit.

[speedie1337]

This pull request improves the script a little bit. Changes:

• Use command -v to check whether a binary is available on the user's system, rather than hash which emits warnings if false.
• Replace all instances of echo with printf, because echo isn't identical on every system. Notably, Gentoo interprets the -e argument as text and as such prints it. In my opinion, echo shouldn't be used in shell scripts.
• Check for the presence of wget on the system. Some distros don't ship wget by default, so in that case we should fail. Ideally a curl fallback would be added but I haven't done that.
• Simplify/improve some code here and there.

[RoootTheFox]

i'll look at this in a bit and make some changes (like adding a curl fallback)

apologies for the late reply, i've been on vacation for a week and didn't actively check github.