Allow passing in an R object to gist_create

[sckott]

Either coerce all objects to json - then when pulled down, jsonlite can convert them back to R objects,

OR

some objects can convert to markdown, like data.frame/matrix to a markdown table

[sckott]

got a start on this in the robjects branch - seems like we could do better though, coercing certain inputs to more useful markdown structures, eg.,

[sckott]

this is done