replace gbdev.gg8.se/forums links to wayback machine mirrors

Author: avivace

src/HuC3.md

@@ -163,4 +163,4 @@ Location | Purpose
 
 ## External links
 
-- Source: [GBDev Forums thread](https://gbdev.gg8.se/forums/viewtopic.php?id=744)
+- Source: [GBDev Forums thread](http://web.archive.org/web/20231003224822/https://gbdev.gg8.se/forums/viewtopic.php?id=744)

src/MBC6.md

@@ -157,7 +157,7 @@ of the protection is stored non-volatile.
 
 ## External links
 
-- Source: [GBDev Forums thread by endrift](http://gbdev.gg8.se/forums/viewtopic.php?id=544)
+- Source: [GBDev Forums thread by endrift](http://web.archive.org/web/20240919224258/https://gbdev.gg8.se/forums/viewtopic.php?id=544)
 - Reference: [Nintendo Power Game Boy Memory cartridge documentation](http://iceboy.a-singer.de/doc/np_gb_memory.html)
   * The NP GB Memory cartridges use a nearly identical flash chip.
     It seemingly only slightly differs in its part number. Therefore,

src/MBC7.md

@@ -134,5 +134,5 @@ enable section as well (0000-1FFF)
 
 ## External links
 
-- Source: [GBDev Forums thread by endrift](http://gbdev.gg8.se/forums/viewtopic.php?id=448)
+- Source: [GBDev Forums thread by endrift](https://web.archive.org/web/20240429225227/http://gbdev.gg8.se/forums/viewtopic.php?id=448)