support "last" option

[masukomi]

I want to ask the changelog manager for the last entry that was created. Or the entries for the last release. All variants would output the markdown that would be used in the generated changelog. Probably without the initial bullet in the single entry version.

Potential interfaces:

changelog_manager -l  # last entry... by creation date? 
changelog_manager --last # ditto
changelog_manager -l=release # entries from the last release
changelog_manager -l=1 # or any number... the last n entries .. by creation date? 

The biggest question is what constitutes the last entry. The last one created? The last one edited? What if they were created in the wrong order? Last release is easy, and useful for populating annotated git tags.