Add implementation of analog TV signal generator (PAL so far)

Quick and dirty Howto:
make && tv/osmotv --sdr-soapy --sdr-tx-gain 60  -r 15000000 -c 21 tx-fubk --sdr-tune-args "OFFSET=-3000000"

src/tv/bas.h

@@ -0,0 +1,25 @@
+
+enum bas_type {
+	BAS_FUBK,
+	BAS_VCR,
+	BAS_IMAGE,
+};
+
+typedef struct bas {
+	double		samplerate;
+	enum bas_type	type;
+	int		fbas;			/* if color shall be added */
+	double		circle_radius;		/* radius of circle in grid units */
+	int		color_bar;		/* show only color bar on all lines */
+	int		grid_only;		/* show only the grid */
+	const char	*station_id;		/* text to display as station id */
+	double		color_phase;		/* current phase of color carrier */
+	int		v_polarity;		/* polarity of V color vector */
+	unsigned short	*img;			/* image data, if it should be used */
+	int		img_width, img_height;	/* size of image */
+	iir_filter_t	lp_y, lp_u, lp_v;	/* low pass filters */
+} bas_t;
+
+void bas_init(bas_t *bas, double samplerate, enum bas_type type, int fbas, double circle_radius, int color_bar, int grid_only, const char *station_id, unsigned short *img, int width, int height);
+int bas_generate(bas_t *bas, sample_t *sample);
+