enhance `taos_options` to support cocurrent calls.
note it still a problem if one thread is modifying a global configuration
while another thread is reading it.

1. the shell should not remove escape sequence \' and \" in a string.
2. `tsParseTime` should not unescape the next string token (this issue
appears after the first issue was fixed).
3. `value[4] != '-'` in `tsParseTime` crashes in rare case if `value[4]`
is in unallocated virtual memory.
4. `operator[x]` and `delimiter[x]` may result in unexcepted behavior
as string is utf-8 encoded and `x < 0` could be true.
5. changes the behavior of `tscGetToken` a little: now, unescaped single
quotation is allowed in double quoted strings and unescaped double quotation
is allowed in single quoted strings.
6. minor performance improvements and other improvements.