Add echo request message parser (refs #55).
Add echo reply message parser (refs #55).
Add echo request message generator (refs #55).
Add echo reply message generator (refs #55).
Add UTF-8 magic comments.
Merge tag '0.5.0' into develop

0.5.0
Add missing 'new features' header line.
Notify Travis results to gitter.im.
Merge tag '0.5.1' into develop

0.5.1
Update changelog.
Assert that hello message_type == 0.
Merge branch 'develop' into feature/of_echo

Conflicts:
	lib/pio.rb
Add Pio::Echo::{Request,Reply}#to_binary.
Merge pull request #67 from trema/feature/of_echo

Feature/of echo
Add :transaction_id and :xid option to Echo::{Request,Reply}#new (closes #55).
Add echo sections.
Fix wording.
Fix wording.
Version bump.
Update changelog.