added Store for contributor DocumentStores
gitignore Store*.bdb
added MercurialDocumentStore

A DocumentStore to read Documents from and store Documents in a
Mercurial repository directory.
tests: added unittests for archiveshub package
bugfix: fixed get_dbSize for MercurialDocumentStore
added hgapi requirement
added UI for adding new contributors
refactored UI for adding new contributors

Main arg is now the directory in which to find the data
Identifier can be explicitly specified with `--id`
Directory can be create if it doesn't already exist using `--create`
added UI for removing contributors
added UI for listing existing contributors
move ConfigStore into stores directory
renamed load.py -> build.py

load: load data from DocumentStores into RecordStore(s)
index: index data already in RecordStore(s)
build: load + index
bugfix: don't init if a sub-dir of a Mercurial repo
added UI for loading from registered contributors
added logging for time taken to load
added UI for loading components
enabled finer control over component loading
fixed component id assignment when not from RecordStore

Fixed identifier assignment for component Records when the parent
is the result of parsing a Document, rather than being fetched from
a RecordStore.
raised minimum log level when loading (>= INFO)
warn rather than error when duplicate records not stored