功能: 字符串向量元素统计

格式:
[s, n] = SymVectorCount(src)
src : 源字符串向量

s : 返回一个src中元素不重复的字符串向量
n : 返回s中对应的统计数据

说明: 
1、本函数主要是统计src中元素出现的次数,统计中严格区分大小写
2、统计结果中以元素个数从大到小进行排列

例子:
s = {SymVectorAppend<矩阵运算\SymVectorAppend>}("s1","a1","s1","a2","s3","s1z","a2","s1")
[g,n] = SymVectorCount(s)//回车得到如下结果,即s1出现了3次, a2出现了2次...
g = 
"s1"
"a2"
"a1"
"s3"
"s1z"
n =
[ 3.00000000000000
  2.00000000000000
  1.00000000000000
  1.00000000000000
  1.00000000000000 ]