update version to 0.18.1

cfg: support resolving $ROOT and $APPNAME variables in command field

The $ROOT and $APPNAME variables can be specified in the Command field of the
.app.toml files and are resolved before execution.

The config version is incremented to 4.

circleci: set POSTGRES_HOST_AUTH_METHOD=trust

The postgres docker image does not allow passwordless admin accounts by default
anymore.
auth_method=trust has to be set to run the postgres instance without admin
password.

set version to 0.17.0

cfg: remove empty sections from Include config

To workaround bug pelletier/go-toml#216 we have to
remove empty FileOutput and DockerImageOutput structs from the buildOutput.
Otherwise the config validation fails because the slices contain FileOutput or
DockerImageOutput structs with empty required fields, like FileOutput.Path

ver: change version to 0.15.0

change version to 0.14

make: create .sha256 checksum files for releases

change version to 0.12

set version to 0.11.3