Document Mustache templates
Use CFEngine_promise_attribute macro
Specify default explicitly
Update information about package version selection.

Related to issue #3314.
select_region clarifications

Adding a section about the lifetime of promises and select_region.
It is very easy to overlook this and as shown by some our acceptance
tests this is leading to confusion.
Removing some uncertainty by adding a see also.
Merge pull request #167 from tzz/feature/mustache

Document Mustache templates
Add some see-also links
Merge pull request #183 from cduclos/select_region_improvements

select_region clarifications
Some editing of select_region clarifications.

Add code markers for keywords, indent example code, shorten heading.
Merge pull request #184 from cduclos/edit_line_improvements

Removing some uncertainty by adding a see also.
Merge pull request #185 from kacfengine/master

Update information about package version selection.
reference/promise-types/files.markdown: Remove mustache renderer.
Add "mailsubject" documentation.
Merge pull request #187 from kacfengine/mailsubject

Add "mailsubject" documentation.
Add details about mon.*_diskfree values
Indicate units, and clarify calculated values
Merge pull request #188 from nickanderson/cleanup/mon_diskfree

Add details about mon.*_diskfree values
files.markdown: special tags to keep Mustache from being eaten
Merge pull request #189 from tzz/master

files.markdown: special tags to keep Mustache from being eaten
Explain Mustache template history.