Dependency Injection: make DI micro-framework a standalone package

[lhaze]

Dependency Injection micro-framework is deserving of its own package. Make preparations to separate it.

Features that are not done yet:

• dependencies of DI (pca.utils.errors) are made standalone first, #83
• support the contextualization of the scope, #78
• scope: thread, #9
• scope: request, #9
• scope: session, #9
• inheritance support while requesting by interface, #20
• generics support while requesting by interface
• prepare quickstart guide
• prepare API docs
• make a standalone repo
• migrate commits & issues to the new repo