All: rename every function from UpperCamelCase to snake_case

This was a mess since I didn't know which to use but now I decided
to go with snake_case :)

libc/stdio/putchar.cpp

@@ -9,7 +9,7 @@
 int putchar(int c)
 {
 #if defined(__is_libk)
-	Kernel::Panic("Please use kprint() instead of stdio");
+	Kernel::panic("Please use kprint() instead of stdio");
 #else
 	abort();
 #endif

libc/stdlib/abort.cpp

@@ -9,7 +9,7 @@ __attribute__((__noreturn__))
 void abort(void)
 {
 #if defined(__is_libk)
-	Kernel::Panic("abort()");
+	Kernel::panic("abort()");
 #else
 	printf("abort()\n");
 #endif