use a precompiled favicon

[garrett]

This commit should eliminate the need for compile-time favicon
generation... and imagemagick, which then pulled in X11 (in Fedora, *)

(The PR should fix #296)

[jberkus]

Thanks! Testing now.

[jberkus]

@garrett fails for me:

identical build/blog/tag/fedora/page=2/index.html
identical build/blog/tag/atomic/page=2/index.html
/usr/local/share/gems/gems/favicon_maker-1.3/lib/favicon_maker/creator.rb:61:in ``': No such file or directory - convert (Errn
o::ENOENT)
from /usr/local/share/gems/gems/favicon_maker-1.3/lib/favicon_maker/creator.rb:61:infetch_image_magick_version' from /usr/local/share/gems/gems/favicon_maker-1.3/lib/favicon_maker/creator.rb:20:in initialize'
from /usr/local/share/gems/gems/favicon_maker-1.3/lib/favicon_maker/generator.rb:41:in`new'

    from /usr/local/share/gems/gems/favicon_maker-1.3/lib/favicon_maker/generator.rb:41:in `block in start'
    from /usr/local/share/gems/gems/favicon_maker-1.3/lib/favicon_maker/generator.rb:38:in `each'
    from /usr/local/share/gems/gems/favicon_maker-1.3/lib/favicon_maker/generator.rb:38:in `start'
    from /usr/local/share/gems/gems/favicon_maker-1.3/lib/favicon_maker/generator.rb:8:in `generate'
    from /usr/local/share/gems/gems/middleman-favicon-maker-3.7/lib/middleman-favicon-maker/extension.rb:19:in `after_buil

d'

[jberkus]

@garrett?

[jberkus]

Given lack of response on this, closing the PR. Please reopen if you can fix the bugs. Thanks.