drop trailing whitespace from header lines

Markdown will mis-parse a header line with trailing
whitespace like:

  ## Subsection ##_

(where the "_" is substituted here to show where the
whitespace would be). This ends up as the section title:

  Subsection ##
[fr] tidy up trailing white spaces
Merge branch 'trailing_spaces'

Conflicts:
	fr/07-customizing-git/01-chapter7.markdown
changed git version, added new example name and fixed bits of text
Updated two Arabic words, and one misspelled English word.
updated some misspellings in Arabic.
[fr] typos in french README
added quotation marks, markups for Chapters and explicit names, and a bit of fine tuning on the text
fixed some funny grammar and changed the hyphens to match the original
[pt-br] Review chapter 1.

Review of Chapter 1 of pt-br, including:
* Fix some typos;
* Fix some grammar errors;
* Normalize plural of acronyms;
* Change creative sentences to something closer to the original;
* Change sentences inconsistent with the book's style;
* Change sentences that don't sound right for a brazilian (me);
* Change translations for some technical terms;
* Remove slangs and made up translations;
* Update Debian commands from the english version;
[ru] fixed some mistypes for chapter 1 in russian translation
[ru] fixed some mistypes for chapter 2 in russian translation
[ru] fixed some mistypes for chapter 3 in russian translation
[ru] fixed some mistypes for chapter 4 in russian translation
No 'git -rm' statement, corrected to 'git rm'.
[es] Translate section 6.1
[pt-br] Translate chapter 5
Inserted missing code tags
Update master
Merge pull request #1 from icemanpro/patch-1

[zh][zh-tw] fix makeebooks to insert figures correctly when lang == zh or zh-tw