manual: use one-line titles instead of two-line titles (trivial)

Asciidoc supports two syntaxes for section titles: two-line titles (title
plus underline consisting of a particular symbol), and one-line titles
(title prefixed with a specific number of = signs).

The two-line title underlines are:
Level 0 (top level):     ======================
Level 1:                 ----------------------
Level 2:                 ~~~~~~~~~~~~~~~~~~~~~~
Level 3:                 ^^^^^^^^^^^^^^^^^^^^^^
Level 4 (bottom level):  ++++++++++++++++++++++

and the one-line title prefixes:
= Document Title (level 0) =
== Section title (level 1) ==

=== Section title (level 2) ===
==== Section title (level 3) ====
===== Section title (level 4) =====

The buildroot manual is currenly using the two-line titles, but this has
multiple disadvantages:

- asciidoc also uses some of the underline symbols for other purposes (like
  preformatted code, example blocks, ...), which makes it difficult to do
  mass replacements, such as a planned follow-up patch that needs to move
  all sections one level down.

- it is difficult to remember which level a given underline symbol (=-~^+)
  corresponds to, while counting = signs is easy.

This patch changes all two-level titles to one-level titles in the manual.
The bulk of the change was done with the following Python script, except for
the level 1 titles (-----) as these underlines are also used for literal
code blocks.
This patch only changes the titles, no other changes. In
adding-packages-directory.txt, I did add missing newlines between some
titles and their content.

----------------------------------------------------------------------------
#!/usr/bin/env python

import sys
import mmap
import re

for input in sys.argv[1:]:

    f = open(input, 'r+')
    f.flush()
    s = mmap.mmap(f.fileno(), 0)

    # Level 0 (top level):     ======================   =
    # Level 1:                 ----------------------   ==
    # Level 2:                 ~~~~~~~~~~~~~~~~~~~~~~   ===
    # Level 3:                 ^^^^^^^^^^^^^^^^^^^^^^   ====
    # Level 4 (bottom level):  ++++++++++++++++++++++   =====

    def replace_title(s, symbol, replacement):
        pattern = re.compile(r'(.+\n)\%s{2,}\n' % symbol, re.MULTILINE)
        return pattern.sub(r'%s \1' % replacement, s)

    new = s
    new = replace_title(new, '=', '=')
    new = replace_title(new, '+', '=====')
    new = replace_title(new, '^', '====')
    new = replace_title(new, '~', '===')
    #new = replace_title(new, '-', '==')

    s.seek(0)
    s.write(new)
    s.resize(s.tell())
    s.close()
    f.close()

----------------------------------------------------------------------------

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/adding-packages-python.txt

@@ -1,8 +1,7 @@
 // -*- mode:doc; -*-
 // vim: set syntax=asciidoc:
 
-Infrastructure for Python packages
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+=== Infrastructure for Python packages
 
 This infrastructure applies to Python packages that use the standard
 Python setuptools mechanism as their build system, generally
@@ -10,8 +9,7 @@ recognizable by the usage of a +setup.py+ script.
 
 [[python-package-tutorial]]
 
-+python-package+ tutorial
-^^^^^^^^^^^^^^^^^^^^^^^^^
+==== +python-package+ tutorial
 
 First, let's see how to write a +.mk+ file for a Python package,
 with an example :
@@ -61,8 +59,7 @@ built.
 
 [[python-package-reference]]
 
-+python-package+ reference
-^^^^^^^^^^^^^^^^^^^^^^^^^^
+==== +python-package+ reference
 
 As a policy, packages that merely provide Python modules should all be
 named +python-<something>+ in Buildroot. Other packages that use the