Clean the doc

[thibautjombart]

The roxygen files as they currently stand are quite messy to read, and it makes error tracking very difficult. We need to clean the doc, remove all superfluous {}, e.g

@details {
bla bla 
\itemize{
  \item{arg:}{this is bla bla a very very long description which is way way way way more than 80 characters}
  \item{anotherarg:}{toto il est beau}
}}

should be

 @details 
bla bla 
\itemize{

  \item arg this is bla bla shorter and 
     on several lines if needed, so that
     we can read it

  \item anotherarg toto il est beau
}

including the lines between items; I have started this on the branch cleandoc