New is now used to create new indexes
Open is used to open existing indexes
calls to Open no longer specify a mapping because the mapping
is serialized and stored along with the index
now can track array positions for field values
stored fields now include this in the key
and the back index now uses protobufs to simplify serialization
closes#73
removed analyzers (these are now built as needed through config)
removed html chacter filter (now built as needed through config)
added missing license header
changed constructor signature of filters that cannot return errors
filter constructors that can have errors, now have Must variant which panics
change cdl2 tokenizer into filter (should only see lower-case input)
new top level index api, closes#5
refactored index tests to not rely directly on analyzers
moved query objects to top-level
new top level search api, closes#12
top score collector allows skipping results
index mapping supports _all by default, closes#3 and closes#6
index mapping supports disabled sections, closes#7
new http sub package with reusable http.Handler's, closes#22
