This commit attaches the mmap-backed roaring bitmaps as storage
to the fragments. Currently snapshotting is not supported from
Pilosa so the WAL will grow indefinitely, however, it is not a
difficult change to make.
This commit refactors the pilosa codebase. It makes several major
changes:
* Removes bitmap handles
* Removes dispatch/hold/transport
* Removes etcd dependency
* Adds consistent hash ring for slice placement
* Refactors parser/lexer
* Adds strong typing to PQL AST
* Flattens package hierarchy
This commit moves the index package to the root. Because pilosa
is an index at its core, it's redundant to have an index
subpackage. It also provides better naming such as `pilosa.Bitmap`
instead of `index.Bitmap`.
