Added support for executing child chunks when knitting up to current lin...

Currently the function for knitting all code up to the current line (`<localleader>ch`) skips any child chunk.

This PR fixes that issue and allows child chunks to be executed as well.

At first I considered readings in the lines from the child document and adding them to the line buffer to be executed all at once, but since the child document treats paths relative to itself, this could cause problems if, for example, the parent and child documents are in different folders and the child document loads a table using a relative path.