Added LangParser as a Maven module
Throw checked ParseException instead of unchecked
IndexOutOfBoundsException
Catching one more IndexOutOfBoundsException
Throw ParseException if the attribute name or value is empty.
Refactoring - added "subscription tree" as a wrapper (POM) parent
artifact for 2 modules: counting tree and langparser.
Fixed a bug - the predicate was not fully removed in unsubscribe()
Fixed a bug (see testCon() test) - if the key already in the tree (the
prefix) and the input of getAllPrefixes() were differing only in the
last character, they were still considered equal