added antlr4 maven plugin, put grammar into the expected directory and created package structure
added implementation of keygroup and some tests
simplified, guarantee non null
simplified recursive lookup
use guava
less redundant names
added recursive put method
first draft visitor based parser
 removed to re-add with capitalized first letter due to hfs+ not being case sensitive
re-add with capitalized first letter due to hfs+ not being case sensitive
implemented all required string escape sequences
multiple type safe visitors, basic test
added convenience getters to KeyGroup
moved remaining visitor methods to inner class
added convenience method for retrieving a list
more tests
added readme
Merge branch 'release/1'