Reorganize fmt and strings; Replace fmt.String_Buffer with strings.Builder

core/os/os_essence.odin

@@ -71,6 +71,10 @@ stdin  := Handle(-1); // Not implemented
 stdout := Handle(0);
 stderr := Handle(0);
 
+is_path_separator :: proc(r: rune) -> bool {
+	return r == '/';
+}
+
 current_thread_id :: proc "contextless" () -> int {
 	return OSGetThreadID(Handle(0x1000));
 }

core/os/os_linux.odin

@@ -203,6 +203,10 @@ foreign dl {
 	@(link_name="dlerror")          _unix_dlerror       :: proc() -> cstring ---;
 }
 
+is_path_separator :: proc(r: rune) -> bool {
+	return r == '/';
+}
+
 get_last_error :: proc() -> int {
 	return __errno_location()^;
 }

core/os/os_osx.odin

@@ -215,6 +215,10 @@ last_write_time :: proc(fd: Handle) -> File_Time {}
 last_write_time_by_name :: proc(name: string) -> File_Time {}
 */
 
+is_path_separator :: proc(r: rune) -> bool {
+	return r == '/';
+}
+
 stat :: inline proc(path: string) -> (Stat, bool) {
 	s: Stat;
 	cstr := strings.new_cstring(path);

core/os/os_windows.odin

@@ -61,6 +61,10 @@ ERROR_FILE_IS_PIPE:           Errno : 1<<29 + 0;
 args := _alloc_command_line_arguments();
 
 
+is_path_separator :: proc(r: rune) -> bool {
+	return r == '/' || r == '\\';
+}
+
 open :: proc(path: string, mode: int = O_RDONLY, perm: u32 = 0) -> (Handle, Errno) {
 	if len(path) == 0 do return INVALID_HANDLE, ERROR_FILE_NOT_FOUND;