Moved chapter titles to the intro pages so that the edit link links
to the right page
Add note about HTTP status code returned when parts of the mget request fails

Fixes #43
Made the distributed-read diagram a bit more explicit.

Closes #47
tiny fix typo
tiny fix typo
Explain that the scroll id can be passed in the body, url or query params

Closes #60
track_score -> track_scores

Closes #61
Typo in the Wikipedia JSON page URL

Typo in URL, preventing the page from opening.
Made changes to Preface.asciidoc
Renamed unwritten chapters to make way for new languages section
Update 15_Create_index_delete.asciidoc

Added an explanation about the special casing of consistency when `number_of_replicas` is set to 1
Update 20_Document.asciidoc

Changed the example JSON document to use `first_name` and `last_name` as per the later examples in the chapter.
Reorganised chapters to make way for Languages
Renamed png/ to images/ for chimera
Fixed bad link
Fixing typo, 'an' should be used when preceding a vowel sound
Fixing typo, 'them' should be used when referring to multiples of something
Fixing typo, 'bu' => 'but'
Fixing typo, added missing closing code quote
Update 45_Mapping.asciidoc

exception, not error.