mkrss improvements needed

[rsdoiel]

The mkrss needs to do a better job. First it should be driven by blog.json where available. Second it needs to produce plain text that is sensible. Right now the RSS I produce is useless because of the overly simple way I create the description. Right now the description will often trip over format required stuff like title and things, those could be skipped in the description. It would be helpful to have a method of pulling the first paragraph so that text like byline or title just confusing the RSS reader (their redundant in the RSS metadata anyway). My current mkrss is sorta of embarrassing.