make lines reformattable

- completely removed the old textbuffer representation (
  https://github.com/shabble/irssi-docs/wiki/Notes-256-Colour#textbuffer-encoding
  )

- textbuffer-formats is an extra module, so if we unhook the signals it
  should go back to the "old way" of storing pre-rendered tex

- design uses cache, original formats and list of arguments

src/fe-text/textbuffer-formats.h

@@ -0,0 +1,22 @@
+#ifndef IRSSI_FE_TEXT_TEXTBUFFER_FORMATS_H
+#define IRSSI_FE_TEXT_TEXTBUFFER_FORMATS_H
+
+#include <irssi/src/fe-text/textbuffer.h>
+
+typedef struct _TEXT_BUFFER_FORMAT_REC {
+	char *module;
+	char *format;
+	char *server_tag;
+	char *target;
+	char *nick;
+	char **args;
+	int nargs;
+	int flags;
+} TEXT_BUFFER_FORMAT_REC;
+
+void textbuffer_format_rec_free(TEXT_BUFFER_FORMAT_REC *rec);
+char *textbuffer_line_get_text(TEXT_BUFFER_REC *buffer, LINE_REC *line);
+void textbuffer_formats_init(void);
+void textbuffer_formats_deinit(void);
+
+#endif