Pgcontents

Fixes missing alembic migration files in the sdist.

Fixes a bug in the `generate_files` utility where a non-notebook file in the database would cause an exception.

- Adds a new `fetch` command to the `pgcontents` CLI for fetching a
single notebook.
- Adds utilities for offline processing of notebooks from the pgcontents
database.
- Adds utilities for encrypting and decrypting notebooks for many users.
- Pegs `notebook` dependency to < 5.0.

Add support for IPython 5.x.

This release adds experimental support for encryption of database notebooks using the `cryptography` library.
- Adds new configurable `crypto` attributes to PostgresContentsManager
and PostgresCheckpoints. `crypto` objects must provide `encrypt`
and `decrypt` methods, which will be called on data being written to
and read from the database, respectively.
- The default `crypto` implementation is `NoEncryption`, which returns
its inputs unchanged.
- The built-in `crypto` implementation is `FernetEncryption`, which
uses `cryptography.fernet` to implement symmetric-key encryption of
all notebooks and files in the database.
- Adds re-encryption utilities to `pgcontents.utils.sync`.

This release adds compatibility with IPython/Jupyter >= 4.0.

Simultaneously supporting IPython 3 and 4 is somewhat tricky, since many of the sub-packages of IPython 3 were broken out into new repositories as part of the transition to the 4.x series. For this reason, `pip install pgcontents` no longer installs **any** version of IPython or Jupyter. Instead, separate `extras` sets are provided for the 3.x and 4.x series.

To install pgcontents in a manner compatible with the latest Jupyter packages, run:


pip install pgcontents[ipy4]


To install pgcontents with the legacy IPython 3.x series, run:


pip install pgcontents[ipy3]


Simply installing `pgcontents` without an extras set will complete successfully, but will trigger an error on any attempt to import the `pgcontents` module.