Add --log-file and --log-level to cmd args options, minor refactoring

fixes #50
Move Server.hs to Main.hs
Move modules (Interpreter, Index, DocTable)

Hunt.Interpreter.Interpreter -> Hunt.Interpreter
Hunt.Index.Index             -> Hunt.Index
Hunt.DocTable.DocTable       -> Hunt.DocTable

fixes #37
Cleanup, documentation, minor refactoring
Use Data.Default with Hunt configuration