readline: add missing documentation, fix documentation format, add README.md (#7683)

vlib/readline/readline.v

@@ -1,43 +1,57 @@
 // Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
 // Use of this source code is governed by an MIT license
 // that can be found in the LICENSE file.
-
-// Will serve as more advanced input method
-// Based on the work of https://github.com/AmokHuginnsson/replxx
-
+//
+// Serves as a more advanced input method
+// based on the work of https://github.com/AmokHuginnsson/replxx
+//
 module readline
 
-// Linux
-// Used to change the terminal options
+// Termios stores the terminal options on Linux.
 struct Termios {
 mut:
-  c_iflag int
-  c_oflag int
-  c_cflag int
-  c_lflag int
-  c_cc [12]int //NCCS == 12. Cant use the defined value here
+	c_iflag int
+	c_oflag int
+	c_cflag int
+	c_lflag int
+	c_cc    [12]int // NCCS == 12. Can't use the defined value here
 }
 
-// Linux
-// Used to collect the screen information
+// Winsize stores the screen information on Linux.
 struct Winsize {
-  ws_row u16
-  ws_col u16
-  ws_xpixel u16
-  ws_ypixel u16
+	ws_row    u16
+	ws_col    u16
+	ws_xpixel u16
+	ws_ypixel u16
 }
 
+// Readline is the key struct for reading and holding user input via a terminal.
+// Example: import readline { Readline }
 pub struct Readline {
 mut:
-  is_raw bool
-  orig_termios Termios // Linux
-  current ustring // Line being edited
-  cursor int // Cursor position
-  overwrite bool
-  cursor_row_offset int
-  prompt string
-  prompt_offset int
-  previous_lines []ustring
-  search_index int
-  is_tty bool
+	is_raw            bool
+	orig_termios      Termios // Linux
+	current           ustring // Line being edited
+	cursor            int // Cursor position
+	overwrite         bool
+	cursor_row_offset int
+	prompt            string
+	prompt_offset     int
+	previous_lines    []ustring
+	search_index      int
+	is_tty            bool
+}
+
+// get_prompt_offset computes the length of the `prompt` `string` argument.
+fn get_prompt_offset(prompt string) int {
+	mut len := 0
+	for i := 0; i < prompt.len; i++ {
+		if prompt[i] == `\e` {
+			for ; i < prompt.len && prompt[i] != `m`; i++ {
+			}
+		} else {
+			len = len + 1
+		}
+	}
+	return prompt.len - len
 }