Merge branch 'v1-8-stable' of https://git-wip-us.apache.org/repos/asf…

…/incubator-airflow into v1-8-stable

Adding .readthedocs.yml

1.8.0 Release

Also tag 1.8.0+apache.incubating

Adding .readthedocs.yml to build docs for 1.7.1.3

Adding .readthedocs.yml to build docs for 1.7.1.3

Adding .readthedocs.yml to build versioned docs

Merge pull request apache#3 from airbnb/plypaul_disable_run_connectio…

…n_pool

Disable connection pool for `airflow run` commands

[AIRFLOW-243] Create NamedHivePartitionSensor

Closes apache#1593 from zodiac/create-NamedHivePartitionSensor

[AIRFLOW-160] Parse DAG files through child processes

Instead of parsing the DAG definition files in the same process as the
scheduler, this change parses the files in a child process. This helps
to isolate the scheduler from bad user code.