Integrate flaterm terminal

kernel/flanterm/README.md

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+# Flanterm
+
+Flanterm is a fast and reasonably complete terminal emulator with support for
+multiple output backends. Included is a fast framebuffer backend.
+
+### Quick usage
+
+To quickly set up and use a framebuffer Flanterm instance, it is possible to
+use the `flanterm_fb_init()` function as such:
+```c
+#include <flanterm.h>
+#include <flanterm_backends/fb.h>
+
+struct flanterm_context *ft_ctx = flanterm_fb_init(
+        NULL,
+        NULL,
+        framebuffer_ptr, width, height, pitch,
+        red_mask_size, red_mask_shift,
+        green_mask_size, green_mask_shift,
+        blue_mask_size, blue_mask_shift,
+        NULL,
+        NULL, NULL,
+        NULL, NULL,
+        NULL, NULL,
+        NULL, 0, 0, 1,
+        0, 0,
+        0
+    );
+```
+Where `framebuffer_ptr, width, height, pitch` and `{red,green,blue}_mask_{size,shift}`
+represent the corresponding info about the framebuffer to use for this given instance.
+
+The meaning of the other arguments can be found in `flanterm_backends/fb.h`.
+
+To then print to the terminal instance, simply use the `flanterm_write()`
+function on the given instance. For example:
+```c
+#include <flanterm/flanterm.h>
+
+const char msg[] = "Hello world\n";
+
+flanterm_write(ft_ctx, msg, sizeof(msg));
+```