Implement Adlib extractor.
Implement Visserijmuseum Zoutkamp.
Add TextielMuseum as a source.
Add documentation for the TextielMuseum and the Visserijmuseum.
Add the production date for textielmuseum.
Keep up with master.
A bit of fefactoring of the AdlibExtractor:

- Removed unnecessary references to OAI
- Added defaults for query ('all'), xmltype ('unstructured') and limit
  (50) attributes, this should simplefy configuration of new sources
- Only allow setting specific 'adlib_*' settings in the
  source_defenition
- Adlib seems to return valid XML, removed the hacky parse function
- Simplified paginating through search results
Fixes for the TextielMuseumItem:

- Don't store date if not present
- Removed print statement
- Removed obsolete namespaces
- Store multiple authors, when present
- Store multiple images, when present
- Include all items in the 'all_text' field
- Use the 'object_number' to find the correct URL of the HTML page
Changes to ZoutkampItem:

- Removed obsolete namespaces
- Store multiple authors, when present
- Include all items in the 'all_text' field

According to the documentation there should be a lot more info available
through the API, but field such as description, date and keyword are not
exposed. I will make an issue for this.
Merge pull request #43 from openstate/breyten-visserijmuseum

Adds Visserijmuseum and TextielMuseum sources