Refactor: clean up naming to be consistent with snake_case

[schicho]

Cleaned up the code to be consistent with snake_case everywhere. Before there was a mixture of diverse naming styles.

Due to modifying almost every file, the line count has gotten quite large. I have split up the changes per .c and corresponding header file into individual commits, to maybe make it a bit more easy to view the changes. Every commit is buildable.

Changes:

• switch to snake_case
• rename functions and variables where sensible
  • rename gc_dvd to simply dvd
• move md5 code into its own directory, just like sha1 and crc32 code
• move some hardcoded values to enums or defines (shutdown or return to HBC, max DAT download size)
• prefix functions in header files consistently

I have not changed the code in md5, sha1 and crc32 as these are libraries, which have been written like that by others years ago and is not core cleanrip code. Would you also handle it that way?

If there are any objections to these changes or need for discussion, let me know.

[emukidid]

Yeah, if you feel like doing this to the entire codebase I don't mind.

[schicho]

Yeah, if you feel like doing this to the entire codebase I don't mind.

That's what I did. You may take a look now. :)