Resolve tidyverse#140.

- Test for frame_matrix() basic functionalities
- Extract the code that parses tribble(...) arguments. Re-use that code for both tribble and frame_matrix

R/tribble.R

@@ -77,9 +77,7 @@ extract_data <- function(...) {
   i <- 1
   while (TRUE) {
     if (i > length(dots)) {
-      out <- rep(list(logical()), length(frame_names))
-      names(out) <- frame_names
-      return(as_tibble(out))
+      return(list(frame_names = frame_names, frame_rest = NULL))
     }
 
     el <- dots[[i]]