Function countLines

countLines(str: string): number
Counts the number of lines in a string.
Parameters
- str: string
  The input string.
Returns number
Number of lines in the string.
Remarks
- Handles Unix (\n), Windows (\r\n), and old Mac (\r) line endings.
Example
```
countLines("a\nb\nc");     // 3
countLines("a\r\nb\r\nc"); // 3
countLines("hello");       // 1
```
- Defined in src/string/fn.ts:154