Add 'matches' function

Takes in a regex and returns a string list of matches. This can be iterated on with a pattern if there are multiple similar matches in the document. Add MIT license attribute to Gemspec. Ignore .DS_Store (Mac file).

My implementation:

I have a .docx document template with many fields in the general form of `{@profile.some_attribute}`. I want anything that looks like that to be replaced with the actual value.

In my `app/controllers/municipalities_controller`:

```ruby
  def export
    # I have a Facade class in app/facades called Profile. This is modeled
    # after Thoughtbot and Sandi Metz's developer rules:
    # http://robots.thoughtbot.com/sandi-metz-rules-for-developers.
    # You could just instantiate a regular model object here.
    @profile = Profile.new( Municipality.find params[:id].titleize) )

    # Initialize DocxReplace with my template, which is stored in lib/assets
    doc = DocxReplace::Doc.new("#{Rails.root}/lib/assets/template.docx",
                               "#{Rails.root}/tmp")

    # Get matches
    matches = doc.uniq_matches(/\{(\@[\w\.]*)\}/)

    # Replace all matches, one at a time, specifying :multiple_occurrences as true.
    # I have to include the curly braces in the first argument to #replace because they
    # are in the template.
    matches.each {|match| doc.replace("{#{match}}", "#{eval match}", true)}
    
    # Write the document back to a temporary file
    tmp_file = Tempfile.new('word_template', "#{Rails.root}/tmp")
    doc.commit(tmp_file)

    send_file tmp_file.path, filename: "#{@profile.muni} Housing Needs Assessment.docx",
                             disposition: 'attachment'
  end
```

In `app/views/municipalities/profile.html.haml`:

```haml
%a.btn.btn-lg.btn-primary{href: export_municipality_path(@profile.muni)}
        Export to Word (.docx)
```

In `config/routes.rb`:

```ruby
...
  resources :municipalities, except: [:index], path: '' do
    ...
    get 'profile',  on: :member
    get 'export',   on: :member
    ...
  end
```