Fixes #232.

Updated gitlab.yml.erb template to include a parameter for issue_closing_pattern.
I'm very new to ruby, so enhancements on this are welcome!
* Note: Backslashes must be escaped in the gitlab.rb string.
Add the first draft of development doc.
#232: Use "single_quote" helper instead of "if" condition
Merge branch 'development_doc' into 'master'

Development doc

First draft of the advice for development setup.

Contains some commands but tried to keep it 'OS-agnostic'.

See merge request !200
Make it clearer where to put your HTTPS key/cert
Add a HTTPS firewall example for Centos 7
Merge branch 'https_docs' into 'master'

Further improve HTTPS docs

See merge request !202
Merge branch 'master' into 'master'

Add issue_closing_pattern to gitlab.rb

This is working for me in adding an issue_closing_pattern value to the generated gitlab.yml.

I'm new at ruby, so forgive me if I've made any mistakes here.

Backslashes in the regular expression used in gitlab.rb must be escaped.

Associated issue: https://gitlab.com/gitlab-org/omnibus-gitlab/issues/232

See merge request !198
Add changelog entry for issue_closing_pattern