func IsValidVarName(v string) bool {
	if len(v) == 0 {
		return false
	}
	for x, r := range v {
		if x == 0 && !unicode.IsLetter(r) {
			return false
		}
		if unicode.IsLetter(r) || unicode.IsDigit(r) ||
			r == tokHyphen || r == tokDot || r == tokUnderscore {
			continue
		}
		return false
	}
	return true
}
IsValidVarName check if "v" is valid variable name, where the
first character must be a letter and the rest should contains only letter,
digit, period, hyphen, or underscore.
If "v" is valid it will return true.
package ini
import (
	"strings"
	"unicode"
)