v0.1.15

Release 0.1.15

Keep the E_ prefix to error codes only

The rename swept up three kinds of name that are not codes.

PIPELINE_STAGES is the list of pipeline stage names, exported and imported by
that name — E_PIPELINE_STAGES broke a public import for nothing.

ATLAS_STRICT, ATLAS_TEST_PG_URL and ATLAS_TEST_MYSQL_URL are environment
variables. Renamed, the integration suites read a variable nothing sets, so
they would have skipped silently forever instead of running against a real
Postgres or MySQL — coverage lost with no failing test to show for it. Three
test-local variables in ream went the same way and are restored too.

A photon comment named two codes in their pre-namespace spelling.

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Changes since v0.1.14.