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.
Merge pull request #480 from laurenrother/2.2.x

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