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 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