cleanup rake routines
deduplicate subgem lists
remove deprecated cache functionality

Conflicts:
	padrino-cache/lib/padrino-cache/legacy_store.rb
use Hash#eack_key
cleanup and improve helpers
refactor test system
allow Padrino::Rendering on stdlib ERB
add travis run for stdlib-erb
use stdlib ERB lazily if no erb gem was bundled
emulate basic Sinatra set for Padrino::Mailer
add button content tag to button_to with block, fixes #1772
remove some deprecations
switch default renderer to none, closes #1133

stdlib ERB rendering still works with :none renderer, ref #1783
fix padrino-admin tests