add line_slice function

docs/utils.md

@@ -11,6 +11,7 @@
   * [convert\_to\_bool](#jc.utils.convert_to_bool)
   * [convert\_size\_to\_int](#jc.utils.convert_size_to_int)
   * [input\_type\_check](#jc.utils.input_type_check)
+  * [line\_slice](#jc.utils.line_slice)
   * [timestamp](#jc.utils.timestamp)
     * [\_\_init\_\_](#jc.utils.timestamp.__init__)
 
@@ -231,6 +232,35 @@ def input_type_check(data: object) -> None
 
 Ensure input data is a string. Raises `TypeError` if not.
 
+<a id="jc.utils.line_slice"></a>
+
+### line\_slice
+
+```python
+def line_slice(data: Union[str, Iterable],
+               slice_start: Optional[int] = None,
+               slice_end: Optional[int] = None) -> Union[str, Iterable]
+```
+
+Slice input data by lines - lazily, if possible.
+
+Accepts a string (for normal parsers) or an iterable (for streaming
+parsers). Uses normal start/stop slicing values, but will always slice
+on lines instead of characters. Positive slices will use less memory as
+the function will attempt to lazily iterate over the input. A negative
+slice parameter will force the function to read in all of the data and
+then slice, which will use more memory.
+
+Parameters:
+
+    data:              (string or iterable) - input to slice by lines
+    slice_start:       (int) - starting line
+    slice_end:         (int) - ending line
+
+Returns:
+    string if input is a string.
+    iterable of strings if input is an iterable (for streaming parsers)
+
 <a id="jc.utils.timestamp"></a>
 
 ### timestamp Objects