Use restrucured GetCaller and PostCaller.

remove error-handler from initialize.

make try_error_handling take a block This way the method can determine itself whether error_handling was successful and call the block if appropriate.

fix error_handler creation paradox In order to function correctly an error handler needs the instance of the caller (GetCaller for example). As the error handler however was supplied when creating the caller this would create an impossible paradox. So we'll use a public-setter for now.

add ability to pass a error_handler to uri-getcall This should allow custom error handling for all types of errors that are not handled by the GetCaller itself.

produce more useful message for UnfollowableRes.

add file-type comment.

Include Errors into GetCaller for UriFetcher.

start extracting uri-get-fetching into class Since a class should be more useful than a collection of loosely coupled methods we'll use an instantiable class for the more complex get-requests.

add mechanism to handle unfollowableness Add a custom errorclass to uri-fetcher in order to detect and handle unfollowable responses. Unfollowable Response in our case actually means two things 1. the response does not have a location header set, which would be needed in order to follow the response to a different location. 2. the response itself is not a response which yields a body suitable for us. suitableness is determined through the overrideable has_actual_content? method.

improve uri fetcher error handling This includes some error classes, a default no-redirections-limit constant (which uses the value 1) and a specific TooManyRedirects error class, which also contains the previous response which we received before it all went to hell.

fix namespacing and method-name for uri-fetcher.

add uri fetcher to fetch corresponding files we can either fetch them to memory or directly to the harddrive.