remove filter option from BoolQuery#append()

[Shinichiro Abe]

filter option is confusing differed from normal TermQuery. use addFilter() instead.

[Shinichiro Abe]

fix #48

→ <<cset cc0a593ca2f8>>

[Shinichiro Abe]

note: now filter accepts Term or Range query. when using a TermQuery on filter, the filter DOES NOT analyze text. we recommend to use String keyword field to the filter.

[Shinichiro Abe]

fix #48. update README.md

→ <<cset 9616fbc2c7bd>>

[Shinichiro Abe]

fix #48. extends->implements

→ <<cset d1112b86e047>>