Minor format changes: hook_civicrm_batchItems.md

Made minor formatting changes to improve appearance of rendered file.

Update extensions.md    "book(s)" to "guide(s)"

close #131 

Changed "book(s)" to "guide(s)" throughout.

NOTE: No change: the two following lines have links with "book(s)" embedded in them.
Line no.	issue
12		[/**books**/volunteer.yml](https://github.com/civicrm/civicrm-docs/blob/master/**books**/volunteer.yml)
101		Go to the [**books** configuration within our publishing system](https://github.com/civicrm/civicrm-docs/tree/master/**books**)

Update index.md changing "book(s)" to "guide(s)"

Close #131 

Changes include "guide book(s)" to "guide(s)" in par. 3 and 4 (lines 8, 10).

Migrated from the following two sources

https://github.com/civicrm/civicrm-buildkit/blob/d20229ac9f63aaf183687157a5e655c953b81f5e/doc/daily-coding.md#housekeeping
https://civicrm.stackexchange.com/questions/17717/how-do-i-upgrade-civicrm-on-a-local-site-that-i-installed-with-buildkit-civibuil/17721#17721

Not adding internal redirects because these pages are so new.

New sections on dev tools and buildkit

Based on discussion here:
https://github.com/civicrm/civicrm-dev-docs/pull/189

Content in it needs to be re-oragnized into multiple other pages. We'll
leave that for another time.

Update index.md, paragraph 2 -- "basic overview" link

In second paragraph remove space between "overview] (https" to read "overview](https:" so that URL does not appear adjacent to "basic overview".

https://wiki.civicrm.org/confluence/display/CRMDOC/Using+the+API

All content here was already in the dev guide so I just created the
redirect.

https://wiki.civicrm.org/confluence/display/CRMDOC/Call+the+CiviCRM+API+from+a+custom+template

All content already existed in Dev Guide, so just needed to create the
redirect.

https://wiki.civicrm.org/confluence/display/CRMDOC/Extension+Review

(There actually was no content in the wiki page which was not already in
the Dev Guide, so the only thing needed here was to create the
redirect.)

Document API joins - closes #125

* They have been moved to the CiviRules Guide:
  https://docs.civicrm.org/civirules/en/latest/
* Close #183

Revise for Legacy OS - Docker Toolbox

Identify two environments:  Docker for Windows / Mac / Linux and Legacy
OS (Windows 7, 8.1, 10 Home Premium).  Provide docker run commeands for
each environment.

Close #184

Close #86

This is to make sure internal redirects are working, as recently
implemented in docs-publisher

Close #181 removed obsolete discussion