Add textsuperscript and textsubscript snippets

Why? Mainly so I can reference them with keyboard shortcuts, also they're long to type. Not too sure about the current prefix though - any suggestions?

snippets/latex.json

@@ -236,6 +236,16 @@
 		"body": "\\textbf{${1:${TM_SELECTED_TEXT:text}}}",
 		"description": "Use a bold font"
 	},
+	"textsuperscript": {
+		"pre": "FSS",
+		"body": "\\testsuperscript{${1:${TM_SELECTED_TEXT:text}}}",
+		"description": "Make text a superscript"
+	},
+	"textsubscript": {
+		"pre": "FBS",
+		"body": "\\testsubscript{${1:${TM_SELECTED_TEXT:text}}}",
+		"description": "Make text a superscript"
+	},
 	/* Math Formatting */
 	"mathrm": {
 		"prefix": "MRM",