AstCompressor.parse -> Node.computeFreqs

Renaming of the method to parse a Lzw dictionary from a BFS tree to the Node
class.
Change of the package name for LzwCompressor.
Merge branch 'master' of https://github.com/aghosn/persistence
TreeTpe -> AstTag

Since Tpe is used for type inside the complier, we changed this name.
NB: TreeTag is already used by Global.
Merge branch 'master' of https://github.com/aghosn/persistence