Add numbers to buffer lines

This directly correlates hard-wrapped lines with the soft lines
they were wrapped from.

Choosing uint here because it doesn't change the size of struct
Line. It doesn't at all matter since buffers only hold 1024 lines
at a time anyway.

buffer.c

@@ -102,6 +102,7 @@ static int flow(struct Lines *hard, int cols, const struct Line *soft) {
 	int flowed = 1;
 
 	struct Line *line = linesNext(hard);
+	line->num = soft->num;
 	line->heat = soft->heat;
 	line->time = soft->time;
 	line->str = strdup(soft->str);
@@ -177,6 +178,7 @@ static int flow(struct Lines *hard, int cols, const struct Line *soft) {
 
 		flowed++;
 		line = linesNext(hard);
+		line->num = soft->num;
 		line->heat = soft->heat;
 		line->time = 0;
 
@@ -203,6 +205,7 @@ int bufferPush(
 	enum Heat heat, time_t time, const char *str
 ) {
 	struct Line *soft = linesNext(&buffer->soft);
+	soft->num = buffer->soft.len;
 	soft->heat = heat;
 	soft->time = time;
 	soft->str = strdup(str);

chat.h

@@ -301,6 +301,7 @@ int uiSave(const char *name);
 enum { BufferCap = 1024 };
 struct Buffer;
 struct Line {
+	uint num;
 	enum Heat heat;
 	time_t time;
 	char *str;