Update sdl2 to 0.32.2

[kolen]

I couldn't built sdl2's dependency rustc-serialize on my machine, it fails with following error

error[E0642]: patterns aren't allowed in methods without bodies
   --> /Users/kolen/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-serialize-0.3.19/src/serialize.rs:147:45
    |
147 |                                             &f_name: &str,
    |                                             ^^^^^^^
...
error: aborting due to previous error

For more information about this error, try `rustc --explain E0642`.
error: Could not compile `rustc-serialize`.

So I updated sdl2 to latest version.

It had breaking changes, especially after 0.30, when Renderer was split into Canvas and TextureCreator. Also, now Texture has lifetime parameter, but it's not possible to store both TextureCreator and Textures into the same struct, because they're self-referencing. Because of this, sdl2 now has unsafe_textures feature, which is, AFAIK, similar to behavior before 0.30, and it's probably safe to use it as long as textures are not deallocated manually, and looks like rustzx does not deallocate textures prematurely.

However, I'm not sure about regressions, as there are lots of changes in sdl2. For me, it runs very slowly in debug version (in release it's ok). Probably I should first build with first working version of sdl2 and compare.

[kolen]

I tried to update just rustc-serialize: it works and is also slow in debug version: #35. It can be applied first before doing full update of sdl version.

[pacmancoder]

FYI: #34 and #35 were merged.

[kolen]

What I've checked:

• Sinclair's Research's ancient test program, everything seem to work, including all 48k keyboard keys
• Shock megademo, border effects and AY music work
• Setting larger --scale
• Kempston joystick

[pacmancoder]

Cool, thanks for the confirmation testing. I can merge this PR after conflicts will be resolved 😄