Update to bsnes v107r4 beta release.

byuu says:

  - bsnes: added video filters from bsnes v082
  - bsnes: added ZSNES snow effect option when games paused or unloaded
    (no, I'm not joking)
  - bsnes: added 7-zip support (LZMA 19.00 SDK)

[Recent higan WIPs have also mentioned bsnes changes, although the higan code
no longer includes the bsnes code. These changes include:

  - higan, bsnes: added EXLOROM, EXLOROM-RAM, EXHIROM mappings
  - higan, bsnes: focus the viewport after leaving fullscreen exclusive
    mode
  - bsnes: re-added mightymo's cheat code database
  - bsnes: improved make install rules for the game and cheat code
    databases
  - bsnes: delayed construction of hiro::Window objects to properly show
    bsnes window icons

- Ed.]

libco/doc/usage.html

@@ -62,6 +62,14 @@ Return handle to current cothread. Always returns a valid handle, even when
 called from the main program thread.
 <hr/>
 
+<code>cothread_t co_derive(void* memory, unsigned int heapsize, void (*coentry)(void));</code><br/><br/>
+Initializes new cothread.</br>
+This function is identical to co_create, only it attempts to use the provided
+memory instead of allocating new memory on the heap. Please note that certain
+implementations (currently only Windows Fibers) cannot be created using existing
+memory, and as such, this function will fail.
+<hr/>
+
 <code>cothread_t co_create(unsigned int heapsize, void (*coentry)(void));</code><br/><br/>
 Create new cothread.<br/>
 Heapsize is the amount of memory allocated for the cothread stack, specified