Mark Rake::AltSystem for deprecation

Also, hide it from documentation because nobody should be looking at it
or using it.
Hide internal methods in Rake::Application
Use Ruby 2 hash syntax in task examples
Do not mention deprecated runtests
Document Rake::EarlyTime methods
Hide Module#rake_extension from rdoc

Users should not know about this or call it
Mark rake/ext/module.rb for removal
Clean up Rake string extension documentation

Mark these extensions as coming from Rake
Ignore Time extensions in documentation
Improve Rake::FileList documentation
Improve FileTask documentation formatting
Marke rake/gempackagetask for removal in Rake 11
Clean up formatting of InvocationChain documentation