Use a common structure for the shopping cart problem

The structure is needed so the HackBulgaria tools can scrape the repo
and put it under students' solutions.
Start the meta programming problems
Add Symbol#to_proc
Add a task about private/protected accessors
Add a Proxy task
Cheat by delegating even more problems to FMI

😚  @mito and @skanev
Fix markdown typo
Fix spacing
Add Module#cattr_accessor task
Add Object#delegate task
Start with the Simple Test draft

Its in Bulgarian for now, so whoever wants to start working on it right
away, can do that. Will describe it in details as I go.
Promotion classes done..now use them..
Merge with upstream to get week 5