Tweaks to w3m.sh to improve TXT version of docs

Make headers and description terms more apparent, by adding
some more regexps into the `sed` that the HTML is piped through
before being sent to `w3m`.

docs/en/tuxpaint-quickstart-guide.txt

@@ -1,8 +1,8 @@
 Tux Paint 0.9.34 Quickstart Guide
 
-Tools (Drawing)
+                            ### Tools (Drawing) ###
 
-🖌Paint
+## 🖌Paint ##
 
   * Choose a brush on the right.
   * Some brushes are animated 🎞, some are directional ✲, some are both.
@@ -10,7 +10,7 @@ Tools (Drawing)
   * Choose a color (see "Colors").
   * Click/tap and drag in the canvas to paint.
 
-⌧Stamps
+## ⌧Stamps ##
 
   * Change categories with the arrow buttons ⇦⇨ near the bottom right.
   * Choose a stamp on the right.
@@ -27,12 +27,12 @@ Tools (Drawing)
   * Some stamps play descriptive sounds; press the headphones 🎧 button to hear
     it again.
 
-⚟Lines
+## ⚟Lines ##
 
   * (See Paint)
   * Click/tap and drag to draw a line.
 
-⭓Shapes
+## ⭓Shapes ##
 
   * Choose a shape on the right.
   * Select whether you want to extend the shape from the center ⧈, or a corner
@@ -40,7 +40,7 @@ Tools (Drawing)
   * Click/tap to position, and drag to set the size of the shape.
   * Drag to rotate it, and click/tap again to add it to the drawing.
 
-🄰Text
+## 🄰Text ##
 
   * Choose a font on the right.
   * Select whether you want the text bold 𝗔 and/or italic 𝘈, using controls
@@ -60,7 +60,7 @@ Tools (Drawing)
       + "AltGr" can be used to quickly access more characters.
       + Left/Right arrows switches keyboard layouts (e.g., "QWERTY" vs. "ABC")
 
-🅰Label
+## 🅰Label ##
 
   * (See Text)
   * Labels float 'above' the drawing; you cannot paint or stamp over them,
@@ -74,7 +74,7 @@ Tools (Drawing)
   * Or, use the 🖑 button near the lower right to "flatten" a label, applying it
     to the canvas; it may no longer be edited with the Label tool.
 
-🪣Fill
+## 🪣Fill ##
 
   * Choose a fill mode on the right.
   * Choose a color (see "Colors").
@@ -90,7 +90,7 @@ Tools (Drawing)
       + Shaped - Fills the area with a gradient that follows the contours of
         the area being filled
 
-🪄Magic
+## 🪄Magic ##
 
   * Choose a magic tool on the right.
   * Change categories with the arrow buttons ⇦⇨ near the bottom right.
@@ -101,26 +101,26 @@ Tools (Drawing)
     bottom right.
   * Some magic tools allow you to choose their color.
 
-🖓Undo
+## 🖓Undo ##
 
   * Use to undo the most recent changes (multiple undo available).
   * Shortcut: [Control]+[Z]
 
-🖒Redo
+## 🖒Redo ##
 
   * Use to redo the most recent undone change (multiple redo available).
   * Shortcut: [Control]+[R]
 
-◪Eraser
+## ◪Eraser ##
 
   * Choose the size and shape of the eraser on the right.
   * Click/tap and drag to erase parts of the picture (solid color, or starter
     or template image).
   * Shortcut: [X] and click/tap in the drawing (not always available)
 
-Tools (Controls)
+                           ### Tools (Controls) ###
 
-🗏New
+## 🗏New ##
 
   * Choose a solid color, starter, or template image to start with.
       + Starters allow drawing "under" a picture (e.g., a coloring book
@@ -131,7 +131,7 @@ Tools (Controls)
   * Click/tap "⤺Back" to abort and return to your current drawing.
   * Shortcut: [Control]+[N]
 
-🕮⮫Open
+## 🕮⮫Open ##
 
   * Choose a previously-saved drawing to open (or export or erase).
   * Click/tap "🕮⮫Open" to open the saved drawing and continue editing it.
@@ -150,7 +150,7 @@ Tools (Controls)
   * Click/tap "🖻⮫🗏Template" to turn the drawing into a new template.
   * Shortcut: [Control]+[O]
 
-🕮⮪Save
+## 🕮⮪Save ##
 
   * Click/tap to save your drawing.
   * If you've saved previously, you'll be prompted whether to overwrite the
@@ -158,19 +158,19 @@ Tools (Controls)
     (a la "File→Save As...")
   * Shortcut: [Control]+[S]
 
-🖶Print
+## 🖶Print ##
 
   * Click/tap to print your drawing.
   * Hold [Alt] or [Option] while clicking/tapping to bring up printer dialog,
     if available.
   * Shortcut: [Control]+[P]
 
-🗙Quit
+## 🗙Quit ##
 
   * Click/tap to quit Tux Paint.
   * Shortcut: [Escape]
 
-Colors
+                                ### Colors ###
 
   * Click/tap to choose a color to use with the Paint, Lines, and Shapes tools,
     and Stamps and Magic tools that support colors.
@@ -194,7 +194,7 @@ Colors
       + Click/tap "🗑Clear" to start over with no mixed colors.
       + Click/tap "⤺Back" to abort and dismiss the color mixer.
 
-Shortcuts while drawing:
+                       ### Shortcuts while drawing: ###
 
   * [Control]+Click/tap - Quick pipette / color picker 💉 access
   * [X]+Click/tap - Quick eraser ◪ access