Implement libusb_get_version() and update libusb manual page.

Approved by:	re (glebius)
Requested by:	swills
MFC after:	1 week

lib/libusb/Makefile

@@ -65,6 +65,7 @@ CFLAGS+=	-I ../../sys
 .endif
 
 # LibUSB v1.0
+MLINKS += libusb.3 libusb_get_version.3
 MLINKS += libusb.3 libusb_init.3
 MLINKS += libusb.3 libusb_exit.3
 MLINKS += libusb.3 libusb_strerror.3

lib/libusb/libusb.3

@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 5, 2014
+.Dd June 16, 2016
 .Dt LIBUSB 3
 .Os
 .Sh NAME
@@ -43,6 +43,10 @@ The
 library contains interfaces for directly managing a usb device.
 The current implementation supports v1.0 of the libusb API.
 .Sh LIBRARY INITIALISATION AND DEINITIALISATION
+.Ft "const struct libusb_version *"
+.Fn libusb_get_version "void"
+This function returns version information about LibUSB.
+.Pp
 .Ft int
 .Fn libusb_init "libusb_context **ctx"
 This function initialises libusb.

lib/libusb/libusb.h

@@ -235,6 +235,15 @@ struct libusb_pollfd {
 	short	events;
 };
 
+struct libusb_version {
+	const uint16_t major;
+	const uint16_t minor;
+	const uint16_t micro;
+	const uint16_t nano;
+	const char *rc;
+	const char *describe;
+};
+
 typedef struct libusb_context libusb_context;
 typedef struct libusb_device libusb_device;
 typedef struct libusb_device_handle libusb_device_handle;
@@ -384,6 +393,7 @@ typedef struct libusb_transfer {
 /* Library initialisation */
 
 void	libusb_set_debug(libusb_context * ctx, int level);
+const struct libusb_version *libusb_get_version(void);
 const char *libusb_strerror(int code);
 const char *libusb_error_name(int code);
 int	libusb_init(libusb_context ** context);

lib/libusb/libusb10.c

@@ -69,6 +69,22 @@ static void libusb10_submit_transfer_sub(struct libusb20_device *, uint8_t);
 
 /*  Library initialisation / deinitialisation */
 
+static const struct libusb_version libusb_version = {
+	.major = 1,
+	.minor = 0,
+	.micro = 0,
+	.nano = 2016,
+	.rc = "",
+	.describe = "http://www.freebsd.org"
+};
+
+const struct libusb_version *
+libusb_get_version(void)
+{
+
+	return (&libusb_version);
+}
+
 void
 libusb_set_debug(libusb_context *ctx, int level)
 {