Implement hafas messages API

.gitignore

client.go

data/hafas_messages/0.html

data/hafas_messages/1.html

data/hafas_messages/10.html

data/hafas_messages/11.html

data/hafas_messages/12.html

data/hafas_messages/13.html

data/hafas_messages/14.html

data/hafas_messages/15.html

data/hafas_messages/16.html

data/hafas_messages/17.html

data/hafas_messages/18.html

data/hafas_messages/19.html

data/hafas_messages/2.html

data/hafas_messages/20.html

data/hafas_messages/21.html

data/hafas_messages/22.html

data/hafas_messages/23.html

data/hafas_messages/24.html