Python prelude module

[Shoeboxam]

Closes #711

This PR addresses comments left in the issue.

The conventional library import would be:

import opendp.prelude as dp

I'm not placing these imports in the __init__.py because adding a new module...

• gives more flexibility to preserve module structure but shorten names
  • I think we should keep module distinctions for transformations, measurements and combinators
  • The prelude makes these available under t, m, c respectively: dp.t.make_clamp(...)
• doesn't pollute the opendp namespace
  • smartnoise and the higher-level api both want entries in the opendp namespace

The name of the new module is prelude because...

• "prelude" is already a common name for when you want to shorten imports
• It implies that imports under this path are aliases, not a separate copy of the code
  • For example, naming it core or base might give the wrong impression

[Shoeboxam]

Current dependencies on/for this PR:

• main
  • PR Python prelude module #730 👈

This comment was auto-generated by Graphite.

[andrewvyrros]

I'm liking the dp prefix with the prelude!