gobbleNumericLiteral() {
		let number = '', ch, chCode;

		while (Jsep.isDecimalDigit(this.code)) {
			number += this.expr.charAt(this.index++);
		}

		if (this.code === Jsep.PERIOD_CODE) { // can start with a decimal marker
			number += this.expr.charAt(this.index++);

			while (Jsep.isDecimalDigit(this.code)) {
				number += this.expr.charAt(this.index++);
			}
		}

		ch = this.char;

		if (ch === 'e' || ch === 'E') { // exponent marker
			number += this.expr.charAt(this.index++);
			ch = this.char;

			if (ch === '+' || ch === '-') { // exponent sign
				number += this.expr.charAt(this.index++);
			}

			while (Jsep.isDecimalDigit(this.code)) { // exponent itself
				number += this.expr.charAt(this.index++);
			}

			if (!Jsep.isDecimalDigit(this.expr.charCodeAt(this.index - 1)) ) {
				this.throwError('Expected exponent (' + number + this.char + ')');
			}
		}

		chCode = this.code;

		// Check to make sure this isn't a variable name that start with a number (123abc)
		if (Jsep.isIdentifierStart(chCode)) {
			this.throwError('Variable names cannot start with a number (' +
				number + this.char + ')');
		}
		else if (chCode === Jsep.PERIOD_CODE || (number.length === 1 && number.charCodeAt(0) === Jsep.PERIOD_CODE)) {
			this.throwError('Unexpected period');
		}

		return {
			type: Jsep.LITERAL,
			value: parseFloat(number),
			raw: number
		};
	}
Parse simple numeric literals: `12`, `3.4`, `.5`. Do this by using a string to
keep track of everything in the numeric literal and then calling `parseFloat` on that string
@returns {jsep.Literal}