Sort out selection tags

[neocotic]

As suggested by an anonymous user, I will add a tag that allows users iterate over any links in the current selection.

The suggested implementation is to add something like the following in to shortcuts.js (might want to renamed this to something more generic now - like content.js - ensuring manifest.json, background.js and Makefile are updated also);

chrome.extension.onRequest.addListener(function(request, sender, sendResponse) {
    var anchors,
        data = {
            text: '',
            urls: []
        },
        contents,
        selection = window.getSelection();
    data.text = selection.toString();
    if (selection.rangeCount > 0) {
        contents = selection.getRangeAt(0).cloneContents();
        if (contents) {
            anchors = contents.querySelectorAll('a[href]');
            for (var i = 0; i < anchors.length; i++) {
                data.urls.push(anchors[i].getAttribute('href'));
            }
        }
    }
    sendResponse(data);
});

This will listen for a request from the background page that will be triggered when the user activates a template. This request will need to wrap the build*Data functions and requires the current tab;

chrome.tabs.sendRequest(tab.id, {}, function (response) {
    // Continue to build data...
});

Since I'm going to be making this request each time it's worthwhile getting the selected text at the same time (as implemented above) so users should also be able access the {selection} tag when using popup/shortcuts.

[neocotic]

Calling the new complex type {selectionLinks} as it is basically just that.

[neocotic]

Will need to update the external guide for writing templates but this has now been implemented and might want to cover this in the FAQ.