Impelement Migraton.set_role method

Task 1004
Implement generator pg_power:install

Task 1004
Update README

Task 1004
Add missing doc

Task 1004
Implement keep_default_role method

Task 1004
Merge remote-tracking branch 'greyblake/1004_execute_migration_as_role' into 1004_execute_migration_as_role

Task 1004
Task 1101

* greyblake/1004_execute_migration_as_role:
  Implement keep_default_role method
  Add missing doc
  Update README
  Implement generator pg_power:install
  Impelement Migraton.set_role method

Conflicts:
	lib/pg_saurus.rb
	lib/pg_saurus/errors.rb
Use the PgSaurus name

Task 1004
Task 1101
Merge IntegraCredit/HornsAndHooves-pg_saurus#3 v2.2.0 'origin/1004_execute_migration_as_role'

Task 1004
Task 1101

* origin/1004_execute_migration_as_role:
  Use the PgSaurus name
  Implement keep_default_role method
  Add missing doc
  Update README
  Implement generator pg_power:install
  Impelement Migraton.set_role method