Add support for enable_line_numbers, start_line_numbers_at and highlight_lines_extra in code blocks.
It is a correct version of pull request #109

Logic of start_line_numbers_at field:

1. The field accepts integer values - fractional values will be converted to integer values, non-numeric values - discarded.
2. The positive value sets enable_line_numbers="true".
3. An undefined value sets enable_line_numbers="false".

Logic of highlight_lines_extra field:

1. The field accepts a single integer value or a set of integer values separated by a comma - fractional values will be converted to integers, not numeric values - discarded.
2. The field is automatically recalculated when you switch to Prosemirror editor or preview from Prosemirror editor.
3. If a set of values is specified in the field, they will be sorted in ascending order.
4. The possibility to specify relative values has been implemented - if, for example, we have a certain piece of code, the numbering of which starts with 37 lines, and we need to highlight the 53rd and 68th lines of code, then in the field we type: "53,68" (without quotes). In the standard DokuWiki editor we will still have absolute values.
5. The ability to specify absolute values, as implemented in the standard DokuWiki editor is also saved - for this we specify negative values. I.e. to highlight, for example, 4 and 7 code stacks, no matter from which line our code begins to number - specify in the field: "-4,-7" (without quotes).
6. If the field start_line_numbers_at is not specified, the numbering will be the same as in the standard DokuWiki editor, i.e. starting with 1.