Implement HTTP functions

[SergioFLS]

As seen in Demon Tiles (ButterscotchRunner/CompatibilityList#112), the game tries downloading a song online before gameplay, but can't because those functions aren't implemented.

• http_get
• http_get_file
• http_post_string

(EDIT:) The following games also use HTTP functions, but seem to be not needed:

• Five Nights at Sonic's 3 (Five Nights at Sonic's Collection) CompatibilityList#68
• Coin Crypt CompatibilityList#70

Might probably use libcurl, though suggestions for other libraries are appreciated.

Other optional stuff that might be nice to have:

• Custom proxy server support (for stuff like revival servers)
• Fake file server that loads files from filesystem/ZIP/WARC (for offline use)
• Extending above, scripting language (Lua?) support for dynamic HTTP content (such as REST APIs)?

[Un1q32]

libcurl is probably the best choice, also all the http stuff should be optional with a compile time flag to disable it, so systems without proper networking (or just systems libcurl doesn't support) can still build.

[iProgramMC]

libcurl and mbedtls are a good fit, IMO. But yes, you should be able to disable it. In fact, I'd dare to say that disabling it should be default. It could open up the runner to malicious games who download files to bad places on the hard drive, such as the personal startup directory.

[Un1q32]

It could open up the runner to malicious games who download files to bad places on the hard drive, such as the personal startup directory.

I might be wrong, but I think games aren't allowed to write outside of either the game directory or the save file directory, so this wouldn't be an issue.