Allow size of highlighted file to be limited

[IanMayo]

User of this library occasionally have to parse huge documents that are 1000s of lines long.

They may wish to have the whole file highlighted. But, they may only wish to have the first 50 (or so) lines highlighted for the output.

We should introduce an optional argument for the HighlightedDataFile constructor. This argument can take these values:

1. 0 - don't do any highlighting. Allow the record method to be called, but don't act on it
2. 50 - highlight the first 50 (for example) lines in the file. Allow the record method to be called, but don't try to highlight anything after 50 lines. The export method should only export the first 50 lines.
3. "ALL" - process all lines in the file

Note: when we're just going to highlight a portion of the datafile, I suggest we do that by only creating elements in the chars structure for those lines. Then, if ever we try to modify a chars cell which is > len(chars) we silently ignore it.

[roman-hrybinchuk]

1 more argument numberOfLines in main class constructor, you can determine number of lines to be showed, by default all lines.