CHANGES IN SIMPLERMARKDOWN 0.0.4:

  NEW FEATURES:

  - `md_figure` and `output_figure` can now echo the commands used to generate the
    figure. Use the arguments `echo` and `results` for that. 

  - Errors with hopefully more informative error messages in case something goes 
    wrong with the calls to pandoc.

  BUG FIXES:

  - Markdown documents without a header block would generate an error. Fixed.

  - Output was truncated for longer blocks of code. Fixed.

  - Expressions such as `iris[, foo := Sepal.Width/Sepal.Length]` were
    'translated' to `iris[, `:=`(foo, Sepal.Width/Sepal.Length)]` in the output.
    Fixed.

  - When pandoc is not installed an empty dummy vignette is generated. This
    prevents warnings on the CRAN machines without pandoc. This should already
    have been working in the previous version except for a bug.