Fix obsolete method name in Pull::Merge
Extract current_branch, upstream and origin

Refactor these methods to be able to use them elsewhere as well.
Add new interface for Editor

Will be used by pull, other refactorings are open for debate.
Add pull create alias pc
First running implementation of Pull::Create

Error handling still to do, otherwise working fine.
Refactor subcommand_execute in Pull

Support commands that don't require an issue as argument at all
Add option to show a created pull request

... directly after it has been opened.
Add comments for error handling in Pull::Create
Catch no arg at all an Pull#handle_help_request
Minor refactor in Show

Extract method show_pull_request and remove param from
honor_the_issue_contract.
Add Pull::Close
Delete unused method in Pull::Create
Minor fix and renaming in Pull::Create

String interpolation was wrong.
Renames a method (show_pull_request) that also exists elsewhere
(Pull::Show)
Don't pollute the editor content with nil.to_s

When there is no match in extract_keyword, do nothing and don't add an
empty string to the content.
Adds method to check for changes in Editor

Useful for editing, where we want to notify the user, when he has done
nothing.
Always unlink in editor - and add a lengthy note

Describes some of the problems with unlinking and hints at a possible
solution.
Add alias pe for pull edit
Implements editing of pull requests in Pull::Edit