Smsplus64 Emulator (#159)

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## Description
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Switch to smsPlus64 (https://github.com/fhoedemakers/smsplus64) from
TotalSMS.


## Motivation and Context
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issue here -->
This emulator, although still WIP (like most others) works with the
plugin system.

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## Types of changes
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- [x] Improvement (non-breaking change that adds a new feature)
- [ ] Bug fix (fixes an issue)
- [ ] Breaking change (breaking change)
- [ ] Documentation Improvement
- [ ] Config and build (change in the configuration and build system,
has no impact on code or features)

## Checklist:
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- [x] My code follows the code style of this project.
- [ ] My change requires a change to the documentation.
- [x] I have updated the documentation accordingly.
- [ ] I have added tests to cover my changes.
- [ ] All new and existing tests passed.

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README.md

@@ -18,7 +18,7 @@ An open source menu for N64 flashcarts.
 * Fully Open Source.
 * Loads all known N64 games (including iQue and Aleck64 ROMs (even if they are byteswapped)).
 * Fully emulates the 64DD and loads 64DD disks (SummerCart64 only).
-* Emulator support (NES, SNES, GB, GBC) ROMs.
+* Emulator support (NES, SNES, GB, GBC, SMS, GG) ROMs.
 * N64 ROM box image support.
 * Background image (PNG) support.
 * Comprehensive ROM save database (including HomeBrew headers).

docs/00_getting_started_sd.md

@@ -22,6 +22,7 @@ Menu currently supports the following emulators and associated ROM file names:
 - **NES**: [neon64v2](https://github.com/hcs64/neon64v2/releases) by *hcs64* - `neon64bu.rom`
 - **SNES**: [sodium64](https://github.com/Hydr8gon/sodium64/releases) by *Hydr8gon* - `sodium64.z64`
 - **Game Boy** / **GB Color**: [gb64](https://lambertjamesd.github.io/gb64/romwrapper/romwrapper.html) by *lambertjamesd* - `gb.v64` / `gbc.v64` ("Download Emulator" button)
+- **SMS** / **GG**: [smsPlus64](https://github.com/fhoedemakers/smsplus64/releases) by *fhoedmakers* - `smsPlus64.z64`
 
 
 ### 64DD disk support
@@ -48,7 +49,8 @@ SD:\
 │        ├── neon64bu.rom
 │        ├── sodium64.z64
 │        ├── gb.v64
-│        └── gbc.v64
+│        ├── gbc.v64
+│        └── smsPlus64.v64
 │
 ├── (a rom).z64
 ├── (a rom).n64

src/menu/cart_load.c

@@ -177,8 +177,8 @@ cart_load_err_t cart_load_emulator (menu_t *menu, cart_load_emu_type_t emu_type,
             save_type = FLASHCART_SAVE_TYPE_FLASHRAM_1MBIT;
             break;
         case CART_LOAD_EMU_TYPE_SEGA_GENERIC_8BIT:
-            path_push(path, "TotalSMS.z64");
-            save_type = FLASHCART_SAVE_TYPE_SRAM_256KBIT;
+            path_push(path, "smsPlus64.z64");
+            save_type = FLASHCART_SAVE_TYPE_NONE;
             break;
     }