Added performance testing against JBuilder

[fterrazzoni]

Results:

                                     user     system      total        real
Jbuilder                         0.560000   0.000000   0.560000 (  0.561676)
BABL                             0.440000   0.000000   0.440000 (  0.445175)
Precompiled BABL                 0.380000   0.000000   0.380000 (  0.375273)

When the template is pre-compiled, BABL is ~ 30% faster than JBuilder. This is very encouraging, given that code generation hasn't been merged yet.

😎😎😎

BABL template :

author = object(:name, :birthyear, :job)

each.object(
    :body, :title,
    author: _.(author),
    date: _.nav(&:iso8601),
    references: _.each.object(:name, :url),
    comments: _.each.object(
        :email, :body,
        author: _.(author),
        date: _.nav(:iso8601)
    )
)

JBuilder template:

json.array! data do |article|
    json.author(article.author, :name, :birthyear, :job)
    json.title article.title
    json.body article.body
    json.date article.date.iso8601
    json.references article.references do |reference|
        json.name reference.name
        json.url reference.url
    end
    json.comments article.comments do |comment|
        json.author(comment.author, :name, :birthyear, :job)
        json.email comment.email
        json.body comment.body
        json.date comment.date.iso8601
    end
end