Candig-ingest

This release introduces

New:
- Log support: All the actions performed by `candig-ingest` are now logged and stored as log files on the same directory where the ingest was called.
- An `--overwrite` flag that allows you to overwrite all existing records with identical `id`. This is especially helpful when you need to pull data from external sources and perform nightly syncs to a candig-server database.
- A `-d` flag that allows you to write the description of a dataset. Note that this flag only has an effect when the dataset has not been created before. This flag will not overwrite existing dataset's description.
- Allow users to specify `localId` as the unique identifier of all clinical records other than `Patient` and `Sample` table.

Fixes:
- Some code styling issues.
- Some unused import issues.

Updates:
- README.

This update does not introduce any backward-incompatible changes.

This release introduces

New:
- An `--overwrite` flag that allows you to overwrite all existing records with identical `id`. This is especially helpful when you need to pull data from external sources and perform nightly syncs to a candig-server database.
- A `-d` flag that allows you to write the description of a dataset. Note that this flag only has an effect when the dataset has not been created before. This flag will not overwrite existing dataset's description.

Fixes:
- Some code styling issues.
- Some unused import issues.

Updates:
- README.

This update does not introduce any backward-incompatible changes.

This release introduces:

- The updated mock data and tier information to accommodate the newly updated candig-server (appropriate for `candig-server>=1.3.0`).

This release introduces:

- Wrap the ingest operations (multiple insertions) within one transaction
- Update readme.rst
- Explicitly prune the mock_data directory to reduce the distribution size.

This release introduces

- Fixed the problem of pip install under Python 3.6+ environment
- Cleaned up the Readme
- Updated certain syntax to be 2 and 3 compatible.

This release introduces a number of updates:

- Due to the change of namespace in the candig-server, references to `ga4gh.*` have been changed to `candig.*`
- Previously, the installation instructions in Readme has a few outdated commands, urls, etc. These have been replaced with the most up-to-date ones.
- Author email has been added.