Adds subversion support to manage spec-repositories

Our team had been using a in house fork of Cocoapods with svn, bzr, and hg spec-repo support. Since #1747 has been closed, I'm porting that code to plugins

$ gem install cocoapods-repo-svn 

Add

$ pod repo-svn add my-svn-repo http://svn-repo-url

Update

$ pod repo-svn update my-svn-repo 

Remove

$ pod repo-svn remove my-svn-repo 

To include your sources in the install phase of your project, do the following:

plugin 'cocoapods-repo-svn', :sources => [
        'https://svn.myrepository.com'
    ]

..

$ rake build

$ rake install

Repo->Remove and Repo->Lint are generic enough to be lifted out of git specific command/repo