Tantivy 0.6.1

• Bugfix #324. GC removing was removing file that were still in u
  seful
• Added support for parsing AllQuery and RangeQuery via QueryParser
  • AllQuery: *
  • RangeQuery:
    • Inclusive field:[startIncl to endIncl]
    • Exclusive field:{startExcl to endExcl}
    • Mixed field:[startIncl to endExcl} and vice versa
    • Unbounded field:[start to *], field:[* to end]