Adding support to switch from Textile to Markdown

This adds a checkbox in the advanced section to allow selecting Markdown as the syntax for release notes. It will switch the parameter "notes_type" to 1 if selected, else 0 is being used as before this change.

It is being ignored when change logs are used as release notes.
Added UTF-8 support for release notes
Merge pull request #7 from dlinsin/release_notes_type

Adding support to switch from Textile to Markdown