Added docs for view engine config and partials support.
Made copy edits.
Fixed formatting of a table.
Added note about Mustache and explained that partials have access to the same data as templates.
Added a note about the possible encoding issues with Mustache tags.
Added that you could use {{{}}}} to avoid default encoding by Handlebars.
Merge pull request #967 from zhouyaoji/docs_handlebar_partials

[doc] Added documentation for using Handlebars partials and information about using Mustache templates that are rendered by the Handlebars engine.