Update predefined getter/setter methods

[fbacall]

For each Entity subclass, decide which methods should be there, and find a way to document them in yard.

See: #18

[paulwalk]

I think this is directly related to this issue, so I won't raise a separate one: the HTML Preview makes use of methods such as name and author which do not work. My workaround is to use a custom template and substitute (e.g.):

metadata.properties['author'] for author metadata.name for name