1. text analysis is now done before the write lock is acquired
2. there is now a pool of analysis workers
3. the size of this pool is configurable
4. this allows for documents in a batch to be analyzed concurrently
as a part of benchmarking these changes i've also introduce a new
null storage implementation. this should never be used, as it
does not actualy build an index. it does however let us go
through all the normal indexing machinery, without incuring
any indexing I/O. this is very helpful in measuring improvements
made to the text analsysis pipeline, which are often overshadowed
by indexing times in benchmarks actually building an index.
by default we now use the pure go boltdb kv store
it is less tested at this point but appears to work
test pass, and moves us closer to the goal of being
able to just "go get" bleve
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
