Add Create command
Add Update command
Use primary_key for create/update rather than hardcoded :id
Initial work on sequel constraint violation errors
Add on_success/on_errors blocks to create/update commands
Allow chaining on command result
Add delete command
Register raw sequel errors for now

Eventually this should be wrapped with an error object that corresponds
to common interface and provides more user-friendly error message
Merge branch 'master' into command-api

Conflicts:
	lib/rom/sql/adapter.rb
Merge branch 'master' into command-api

Conflicts:
	Gemfile
	spec/shared/users_and_tasks.rb
Update command-api to use commands.try {}
Catch sequel errors and re-raise as ConstraintError
Update spec
Fix spec for jruby
DRY up commands
Bump sequel