Use RequestUrl in Searchable

- Add RequestUrl#pagination_params
Add SearchResultsCollection

- Mix in Enumerable
- Support paged search result queries
- Make sure names and methods are clear
- Do not request records beyond available records
Use `if` condition after #search_again for readability
Deleted redundant code
Set defaults for pagination in RequestUrl
Replace SearchResults with SearchResultsCollection

- Add SearchResultsCollection.from_json
- Make variables and methods in Searchable easier to read
Change default number of search results returned to 500
Add SearchResultsCollection#each_page
Capture last response on Connection.get

- Simplify logic in .get
- Use self.response in #authentication_failed?
Add support for record ids and id ranges via RequestUrl#ids
Extract resource methods into module
Create default get options and derive search defaults from it
Fix bad helper method call in test
Move URL builder method into Getable

This should be using the RequestUrl class
Add OrderCollection.get
Merge pull request #21 from allolex/pagination

- Adds pagination support in searches, so search results are lazily loaded based on your results page size.
- Adds OrderCollection.get