Fixed blog_url not returning & rake setup_github_pages failing

When executing `rake setup_github_pages`, an error tells that `url` don't exist. The reference to that variable has been changed to a call to `blog_url`.

The function `blog_url` was not returning anything, failing to properly write the `_config.yml` file. It now does return what should have.
Fixed blog_url when user contains uppercase letters
Made blog_url becalled just once...

...and stored in the `url` variable.
Update gist tag url to githubusercontent.com
fix script_url_for url bug
Merge pull request #1567 from howiehu/fix-gist-url-bug

Update gist tag url to githubusercontent.com
Refactoring addSidebarToggler()
Merge pull request #1586 from simonewebdesign/master

Refactoring addSidebarToggler()
Initial update to be compatible with Jekyll 2
Added jekyll-sitemap, jekyll-date-format, and updated gems
No longer including Gemfile.lock. Turns out that was a bad idea.
Merge pull request #1589 from imathis/jekyll-2

Jekyll 2.0 compatability
Replaced date plugin with jekyll-date-format
Removed date plugin, added excerpt separator default
Update `paginate_path` comment based on default value
Merge pull request #1592 from yous/patch-4

Update `paginate_path` comment based on default value
Fixes load path issues with ruby-based git credential helpers

Otherwise, we get errors like this (with boxen, e.g.):

```
/opt/boxen/bin/boxen-git-credential:23:in `require': cannot load such file -- boxen/config (LoadError)
        from /opt/boxen/bin/boxen-git-credential:23:in `<main>'
Username for 'https://github.com':
```
Merge pull request #1609 from alindeman/patch-1

Fixes load path issues with ruby-based git credential helpers
.gitignore Gemfile.lock per previous commit

Gemfile.lock was removed in a previous commit, should be ignored so it doesn't get committed again.

https://github.com/imathis/octopress/commit/06c04397053e46fe02fcecce589a2de76d21e160
Merge pull request #1617 from nickhammond/patch-1

.gitignore Gemfile.lock per previous commit