Fix man page and usage()

Man page was repeating -f option, the second time instead of -i,
and this option was lost in usage() message. This patch also indent
the output of usage().

st.1

@@ -42,7 +42,7 @@ The form is [=][<cols>{xX}<rows>][{+-}<xoffset>{+-}<yoffset>]. See
 .BR XParseGeometry (3)
 for further details.
 .TP
-.B \-f
+.B \-i
 will fixate the position given with the -g option.
 .TP
 .BI \-o " file"

st.c

@@ -3870,8 +3870,8 @@ run(void) {
 void
 usage(void) {
 	die("%s " VERSION " (c) 2010-2014 st engineers\n" \
-	"usage: st [-a] [-v] [-c class] [-f font] [-g geometry] [-o file]" \
-	" [-t title] [-w windowid] [-e command ...]\n", argv0);
+	"usage: st [-a] [-v] [-c class] [-f font] [-g geometry] [-o file]\n"
+	"          [-i] [-t title] [-w windowid] [-e command ...]\n", argv0);
 }
 
 int