Embed only part of a file by specifying start and end line numbers

[lukehorvat]

First of all, thanks for your good work on this plugin.

Lately, I've been thinking that it would be cool if you could embed only small parts of individual files i.e. from line A to line B. Ideally, this feature would be enabled by specifying optional start and end line number parameters in the shortcode.

[gist id=546764 file=file.txt start=4 end=12]

And if one does not specify a start or an end, it defaults to the beginning or end of the file respectively.

Looking at your code, on line 116 you do this:

$gist .= htmlentities($fileInfo['content']);

I don't have any familiarity with PHP, but from what I can assume, htmlentities() converts the file contents to a single string containing HTML. So, I'm thinking you could simply split the string on <br/> (or \n if you do it before calling htmlentities()) to get an array of individual lines, get the sub-array from index start to end, and then convert that sub-array back to a string and assign it to the $gist variable.

What do you think?