Allow disabling the automatic use of our internal swtfb client by setting an env (#118)

* Check env when using Framebuffer::new() or Default trait to auto-select old way

This should ensure that binaries built using this version are fixable without
recompiling should issues with our current rm2fb client arise.

* Fix compilation issue

Sorry, but my pc has a billion toolchains and I'm not sure which one right now compiles correctly

* Update src/framebuffer/core.rs

---------

Co-authored-by: Pierre Fenoll <pierrefenoll@gmail.com>

Author: LinusCDE

src/framebuffer/core.rs

@@ -50,7 +50,13 @@ impl Framebuffer {
         let device = &*device::CURRENT_DEVICE;
         match device.model {
             Model::Gen1 => Framebuffer::device(device.get_framebuffer_path()),
-            Model::Gen2 => Framebuffer::rm2fb(device.get_framebuffer_path()),
+            Model::Gen2 => {
+                // Auto-select old method still if env LIBREMARKABLE_FB_DISFAVOR_INTERNAL_RM2FB is set affirmatively
+                match std::env::var("LIBREMARKABLE_FB_DISFAVOR_INTERNAL_RM2FB").ok() {
+                    Some("1") => Framebuffer::device(device.get_framebuffer_path()),
+                    _ => Framebuffer::rm2fb(device.get_framebuffer_path()),
+                }
+            }
         }
     }