Scrape options from a code block
scrape_opts(
  x,
  envir = list(),
  def = list(),
  all = TRUE,
  marker = "=",
  allow_multiple = FALSE,
  narrow = TRUE
)data
environment from $ENV
default values
return all options, even those that are not in def
assignment operator; used to locate lines with options
if TRUE, the list with replicate names
will be reduced
logical; if TRUE, only get options on lines starting 
with >>
list with elements x (the data without options) and named 
options  as specified in the block.