Plugin install method now obsolete.

Superceded by rake task.
Fix path
Whitespace changes.
First draft of new theme editing section
track what's been included/missed from docs/ dir
fix bad links to .md docs: should be code.alaveteli pages
delete redundant anchor tag (Jekyll autogenerates it)
markdown: remove space to preserve double hyphen
add postfix MTA setup instructions/example

from doc/INSTALL-postfix.md
Update the AMI info
rename installing/exim4 to installing/email

because it's no longer just about exim but also postfix.
This commit includes updating links in the docs to the new page.
Fix some syntax/naming issues.
Fix link and whitespace.
add Rails to glossary
Merge branch 'theme-updates' into gh-pages
add Sass to glossary
Merge branch 'gh-pages-fix-branchname' into gh-pages
Fix link
add deployment to docs, update install pages accordingly

Also added glossary entries for dev/staging/production.
The deployment text is from doc/DEPLOY.md which will can be removed
if this goes live into code.alaveteli.org
add setting STAGING_SITE to dev/staging/production defs

this sets the production environment in Rails, nice to have this documented now :-)