Flesh out reference documentation for the parse_qcodes function

Adds a bit more context to the parse_qcodes function documentation. We need more
complete documentation in order to publish to CRAN.

The updated documentation talks a little bit more about how this function works,
and provides a couple of examples.

I moved the majority of the description into the details. This makes the
description a bit more consise while preserving the details in the appopriately
named details section.

See: #209

R/parse_qcodes.R

@@ -1,17 +1,41 @@
 #' Parse coded text
 #'
-#' Take a text document containing coded text of the form:
-#' "stuff to ignore (QCODE) coded text we care about (/QCODE){#qcode} more stuff to ignore"
-#' and turn it into a dataframe with one row per coded item, of the form:
-#' docid,qcode,text
+#' Take a data frame of coded text documents and return a data frame of the
+#' codes captured within.
 #'
-#' Replaces newline characters with an HTML "br" in the captured text
-#' returns an empty dataframe (no rows) if no qcodes were found.
+#' This function takes a text document containing coded text of the form:
+#' \preformatted{"stuff to ignore (QCODE) coded text we care about (/QCODE){#my_code}
+#' more stuff to ignore"} and turns it into a data frame with one row per coded
+#' item, of the form: \code{docid,qcode,text}
 #'
-#' @param x A data frame containing the text to be coded; requires columns "doc_id" and "document_text"
+#' \code{parse_qcodes} assumes that it is being passed a data frame, the
+#' \code{\link{parse_one_document}} function is called to do the heavy lifting
+#' extracting the coded text from the \code{document_text} column.
+#' 
+#' Newline characters are replaced with an HTML \code{<br>} in the captured text.
+#' 
+#' If no valid qcodes are found, \code{parse_qcodes} returns an empty data frame
+#' (no rows).
+#'
+#' @param x A data frame containing the text to be coded; requires columns
+#'          "doc_id" and "document_text"
 #' @param ...  Other parameters optionally passed in
+#' @return If the data frame contains coded text in the \code{document_text}
+#'         column, output will be a data frame with three columns: "doc",
+#'         "qcode", and "text".
+#'
+#'         The "doc" column is the corresponding "doc_id" value from the input
+#'         data frame.
+#'
+#'         "qcode" is the code that the captured text was marked up with.
+#'
+#'         "text" is the text that was captured.
 #' @examples
-#' unlink("./_my_qcoder_project", recursive=TRUE)
+#' parse_qcodes(my_documents)
+#'
+#' # Data frames can be piped into this function
+#' my_documents %>%
+#'   parse_qcodes()
 #' @export
 
 parse_qcodes <- function(x, ...){