Gmail Github Issue userscript. Adds a "+Issue" link at the top of Gmail email threads that will create a new Github issue from all expanded emails in that thread. Substitute the desired issue repository for the default one at the top of the file.

GmailGithubIssue.user.js

// ==UserScript==
// @id          gmailgithubissuescript@userscripts.org
// @name        Gmail GitHub Issue
// @version     1.2
// @release     2014-10-29
// @author      Benjamin Harris
// @namespace   gmailgithubissuescript@userscripts.org
// @description Create a GitHub issue from Gmail
// @include     https://mail.google.com/mail/u/*
// @match       https://mail.google.com/mail/u/*
// ==/UserScript==

var repository = 'totango/main';

// INSERT BUTTON
function insertButton() {
    var $container = document.getElementsByClassName('ade')[0];
    var $button = document.createElement('span');

    $button.class = 'hk J-J5-Ji';
    $button.innerHTML = '<span class="hk J-J5-Ji">' +
        '<div class="T-I J-J5-Ji T-I-JN L3" role="button" data-tooltip="Create a GitHub Issue" aria-label="Create a GitHub Issue">' +
        '<span class="SD"><a id="create-github-issue" href="#" target="_blank">+Issue</a></span>' +
        '</div>' +
        '</span>';
    $container.appendChild($button);

    document.getElementById('create-github-issue').onclick = function() {
        var email = getEmail();
        this.href = 'https://github.com/' + repository + '/issues/new' + '?title=' + encodeURIComponent(email.title) + '&body=' + encodeURIComponent(email.body);
    };
}

// GET EMAIL INFO
function getEmail() {
    var email = {};
    email.title = document.getElementsByClassName('ha')[0].getElementsByTagName('h2')[0].innerText;
    email.body = '';

    var $notes = document.getElementsByClassName('ii gt');
    var $note, author;
    for (var i = 0; i < $notes.length; i++) {
        $note = $notes[i];
        if ($note.style.display !== 'none') {
            author = $note.parentElement.getElementsByClassName('iw')[0].innerText;
            email.body += '\n' + Array(20 + 1).join('=') + '\n' + author + '\n' + Array(10 + 1).join('-') + '\n';
            email.body += $note.innerText;
            email.body += '\n\n';
        }
    }
    email.body = email.body.replace(/\n{3,}/img, '\n\n\n').trim();

    return email;
}

// HANDLE INSERTION LOGIC
function setupScript() {
    if (document.getElementsByClassName('ade').length > 0) {
        insertButton();
    }
}

// :::::BEGIN APPLICATION:::::
(function() {
    console.log('Running Gmail Github Issue userscript!');
    window.onhashchange = setupScript;
}());