view: add infrastructure to iterate through cursor columns

The number of columns i.e. maximal number of cursors located on the
same line can be obtained by view_cursors_column_count.

Column addressing is zero based, valid indexes are [0, max-1].

Assuming there is a cursor on every letter:

 a
 b c
 d e f
 g h
 i

max column would be 3, and the following would iterate over the
cursors forming the second column [c, e, h]:

 for (Cursor *c = view_cursors_column(view, 1); c; c = view_cursors_column_next(c, 1))
   ...

1 files changed, 7 insertions, 0 deletions

diff --git a/view.h b/view.h
index e408cf7..6447032 100644
--- a/view.h
+++ b/view.h
@@ -179,4 +179,11 @@ Filerange view_selections_get(Selection*);
 void view_selections_set(Selection*, Filerange*);
 Text *view_text(View*);
 
+/* get number of columns, that is maximal number of cursors on a line */
+int view_cursors_column_count(View*);
+/* get first cursor in zero based column */
+Cursor *view_cursors_column(View*, int column);
+/* get next cursor (i.e. on another line) in zero based column */
+Cursor *view_cursors_column_next(Cursor*, int column);
+
 #endif