Add <!--IMAGE-LINK--> keyword for templates

[CharlesNepote]

To have more power in the templates, <!--IMAGE-LINK--> would provide the link to the image shown: .llgal/scaled_IMG_3832.JPG for example.

To let it work, I added a line in llgal.in right after line 1888:
$line =~ s/<!--IMAGE-LINK-->/$entry->{scaled_url}/g ;

I can see many use cases for it:

• add a "download image" link
• use another HTML code than the one provided by
• etc.

I don't know if there is more work to implement it, except the documentation. I can build a pull request if you agree with it.

[bgoglin]

Sure, that's easy to add, so why not?
Regarding documentation, you just need to add it to llgal.1 (likely right before ).
If you can write the code, test it, and submit a PR, that'd be great.

[CharlesNepote]

There was a little alert "Use of uninitialized value in substitution iterator" so I modified the previous code and also introduce two keywords instead of one, SCALE-IMAGE-LINK and FULL-IMAGE-LINK as is:

$line =~ s/<!--SCALED-IMAGE-LINK-->/$entry->{scaled_url}/g if defined $entry->{scaled_url};
$line =~ s/<!--FULL-IMAGE-LINK-->/$entry->{url}/g if defined $entry->{url};

I'll modify llgal.1 dans make a pull request if you agree with this proposition.