v0.2.8

Adds Settings.address, user can specify listening address.
Openapi docs allows specifying source path.
Fix configure.getOrdefault's bug.
Adds more documents.
Adds more API docs.
Changes import path, allows import prologue/middlewares instead of
import prologue/middlewares/middlewares. Rename validate to validater. Supports import prologue/auth, import prologue/auth, import prologue/middlewares, import prologue/openapi, import prologue/security,
import prologue/signing and import prologue/validater.
Moves signing from the core directory.