vis: implement gJ like behavior

The behavior is not exactly the same because vim preserves any
existing white spaces wihle we remove existing ones but do
not insert additional ones.

The vim behavior (essentially only deleating new lines) can be
achived using something like:

 :x/\n/d

Close #374

1 files changed, 1 insertions, 0 deletions

diff --git a/vis.h b/vis.h
index 56bf17b..91f9868 100644
--- a/vis.h
+++ b/vis.h
@@ -202,6 +202,7 @@ enum VisOperator {
  * the expected varying arguments are as follows:
  *
  *  - VIS_OP_FILTER     a char pointer referring to the command to run
+ *  - VIS_OP_JOIN       a char pointer referring to the text to insert between lines
  */
 bool vis_operator(Vis*, enum VisOperator, ...);