Secedgar

Many breaking changes, as this update does a lot of restructuring.

- Rename ``filings.py`` to ``company.py`` (and respective ``Filings`` class to ``CompanyFilings``).
- Rename ``master.py`` to ``quarterly.py`` (and respective ``MasterFilings`` class to ``QuarterlyFilings``).
- Rename ``filings`` subdirectory to ``core`` to avoid confusion.
- Create ``ComboFilings`` class that wraps around ``QuarterlyFilings``, ``DailyFilings`` given 2 dates.
- Create ``filings`` factory that returns the correct class based on user inputs. Returns one of ``ComboFilings``, ``QuarterlyFilings``, ``DailyFilings``, ``CompanyFilings``.
- Add many more types to ``FilingType`` enum. Switch to csv table for details.
- If no filings found for ``DailyFilings`` or ``MasterFilings`` after finding that other filings that do not match the criteria exist, then raise a ``NoFilingsError`` instead of a ``ValueError``.

- Add `user_agent` argument to `NetworkClient`
- Bypasses CIK lookup calls to SEC if the provided argument is already a CIK.

- Gets rid of unnecessary `AbstractClient`.
- Flattens directory structure. The `exceptions`, `cik_lookup`, and `utils` have been moved to the main package directory.
- Removes `cik_map` module in favor of single `cik_lookup` module which now houses `get_cik_map`.
- Slightly changes functionality of `get_cik_map` to return single dictionary.
- Rename internal `_get_cik` to `_get_cik_from_html`.

- Fixes bug where `get_response` does not break after validating response (thanks to abbadata!)
- Fixes bug where `get_response` sleeps even after success
- Remove `pause` from `NetworkClient` initialization in favor of optional `backoff_factor` that relies on urllib3 retry module.

* Adds asynchronous requests, downloads are now 10x faster! (big thanks to reteps for this one!)
* Adds ``download_all`` option to ``save`` method, allowing for bulk downloads. Uses threaded extraction and renaming of files. (reteps)
* Adds ``dir_format`` and ``file_format`` options to filings ``save`` method. (reteps)
* Adds :class:`secedgar.parser.MetaParser` and ``extract`` method to :class:`secedgar.filings._index.IndexFilings`. (reteps)
* Adds SC 13G, SC 13G/A, SC 13D, and SC 13D/A filing types to ``FilingType``. (jackmoody11)

* Adds ``entry_filter`` property to ``secedgar.filings._index.IndexFilings`` to help filter out filings from day or quarter that aren't needed (thanks to reteps!)
* ``secedgar.filings.cik_lookup.CIKLookup`` tries to use ``secedgar.utils.cik_map.get_cik_map`` first when looking up tickers/company names (regardless of whether tickers are upper or lowercase)
* Adds validation to ``secedgar.utils.cik_map.get_cik_map`` to ensure correct key options are being used
* ``secedgar.client.network_client.NetworkClient`` now pauses at the end of request as well if `pause` is given.