Adds "Release Notes/Known Bugs" to Changelog, updates file format to markdown, standardizes the format of previous entries

Per a request to have initial release notes that specifically listed known issues for this PE 3.2 release, and barred by time constraints from automating a pull from open issues in JIRA, this commit adds a Release Note and Known Bug section to the Changelog for the imminent 3.2 release. As it will display on the Forge, updates file type to markdown and standardizes previous entries. Adds template for release notes to be filled in later.
Cleans up first entry formatting in changelog

Somehow I just totally missed that the very first changelog entry wasn't formatted at all.
Merge pull request #660 from laurenrother/1.0.x

Adds "Release Notes/Known Bugs" to Changelog, updates file format to markdown, standardizes the format of previous entries