A bit of refactoring

Twelve lines of code less and only two more
A bunch of fixes and modifications added:

- vendor dir is set as a default as it was described in #16
- @assets_path is now just '/assets' by default as Bower doesn’t just handle JavaScript libraries: it will manage any packages, even if that means HTML, CSS, or images.
- added missing :name option for BowerRails::Dsl#dependencies_to_json method as it is needed for Bower 1.0.0
- added BowerRails::Dsl#write_dotbowerrc to use .bowerrc as a native tool for managing assets' directory
- fix for BowerRails::Dsl#js method:

Before it was like:

  @groups = ["lib"] if @groups.empty?

  @groups.each do |g|
    g_options = Hash === g.last ? g.pop : {}
    assets_path = g_options[:assets_path] || @assets_path

    g_norm = normalize_location_path(g.first,assets_path)
    @dependencies[g_norm] ||= {}
    @dependencies[g_norm][name] = version
  end

But you call Array#last and Array#first for the instance of String as g is a String in @groups.each block

Now it is like:

  @groups = [["vendor", {}]] if @groups.empty?
Fixed mess with groups and Railties now add assets paths dynamically, according to user's custom assets_path
Readme updated
Setting default assets_path if it is not specified by user
DRYing BowerRails::Dsl
Additional fixes

- using .bowerrc for managing bower directories with plain bower.json
- using before_initialize instead of after_initialize at bower-rails/railties.rb
- group.last instead of group.pop
Merge pull request #24 from SergeyKishenin/patch-1

A bunch of fixes and modifications added